Low beams keep burning out.
Posted by: tfabris
Low beams keep burning out. - 02/12/2007 06:28
Before I call CarTalk, I'd like some brainstorming ideas.
- 1995 Oldsmobile Achieva owned by Vixy.
- Car *HAS* been taken to the local Olds dealership in an attempt to solve the problem, they just replace the burned out bulbs and don't find anything else wrong.
- Bulbs keep burning out extremely fast. Prior times it took on the order of weeks or a couple of months. But the last time, both bulbs stopped working almost immediately: Replaced bulbs, they worked long enough to look and see that they were working, then the car was moved into and out of a driveway the next day, then when we went to move it back into the driveway the third day, both bulbs were burned out again. No long-term use, and bam, they're bad again.
- Ruled out general case of bad bulbs, because they are burning out simultaneously each time. And this has gone through multiple repeats of the issue, with different amounts of time between each one.
- Bulbs are halogens. They are the kind where you have both the low and the high beam contained within the same actual bulb itself. When you look at the bulbs in a cursory fashion, they don't look particularly bad. But when you look very close, you can see the difference between the highbeam filament which looks fine, and the low beam filament which looks blobby and slightly melty (but not blackend per se).
- Vixy thinks but cannot confirm for sure that the lowbeam burnouts are somehow related to the highbeam usage. For example, they worked fine for a few months until she turned on the high beams and then she noticed they were out. However she can't be sure; she concedes that the last time she might have turned on the high beams because the low beam bulbs were already burned out and she was just trying to make it brighter.
- High beams always work fine and do not burn out. Only the low beam filaments in the same bulbs burn out.
- Clearly there is some kind of an electrical problem, but where to start looking? There are perfectly good fuses in the proper places and of the proper ratings.
Ideas?
Diagnostic questions and tests welcomed: Between me and Vixy, we'll try them out and perhaps narrow down the issue.
Posted by: music
Re: Low beams keep burning out. - 02/12/2007 08:27
I wonder if one of the fuses, though of the proper rating, is a defective fuse or perhaps installed in such a way that something is shorting across the terminals.
Though, if that is the case, it just means that you'll be blowing fuses all the time instead of headlights. Albeit cheaper, though equally annoying.
Do you have access to a shop manual or wiring diagram of the car?
I wonder if there is some sort of transformer or voltage converter feeding the headlight circuit -- though I'm fairly certain sealed beam Halogens run off straight 12V DC.
Another thought is that a flaky alternator could be injecting noise spikes into the system that wouldn't trigger a slow blow fuse.
Have you checked the Empeg FAQ entry about tracking down grounding problems?
Maybe an iffy contact in the headlight switch or somewhere in the wiring harness could be causing the lights to jiggle on-and-off rapidly enough that the light remains fairly constant but you get a lot of on/off transients through the filament while driving.
If all else fails, maybe you could install tonyc's old breaker panel in series with your fusebox....
Posted by: mlord
Re: Low beams keep burning out. - 02/12/2007 11:56
Bad/blown
voltage regulator.
Fortunately, that should be a simple user-replaceable part.
Check the vehicle manual to find out for sure.
EDIT: Hmmm.. it seems that many places overprice the regulator,
in hope that you'll just buy an entire new/refurb. alternator instead
(the regulator is usually located inside the alternator).
/EDITCheers
Posted by: larry818
Re: Low beams keep burning out. - 02/12/2007 12:36
I'm thinking this probably isn't a voltage problem. Car electrical system vary from 12 to 15 volts when operating, but volts high enough to kill the headlights would be killing other things as well.
On GM stuff, the headlights are protected by an "automatic resetting circuit breaker". I'm betting this breaker is old and corroded.
Have you tried an ohm measurement of the low beam filiment after removing the bulb? See if it's really dead, or you're just replacing bulbs while the breaker resets...
Also, connect a volt meter to the headlight socket and rev the motor. I'll bet the volts don't go over 15, but if they do, then it's the voltage regulator.
Posted by: mlord
Re: Low beams keep burning out. - 02/12/2007 12:43
Quote:
On GM stuff, the headlights are protected by an "automatic resetting circuit breaker". I'm betting this breaker is old and corroded.
If it were that, then high-beams wouldn't work either. But they do work.
Posted by: mlord
Re: Low beams keep burning out. - 02/12/2007 12:46
Quote:
Bad/blown voltage regulator.
Fortunately, that should be a simple user-replaceable part.
Check the vehicle manual to find out for sure.
EDIT: Hmmm.. it seems that many places overprice the regulator,
in hope that you'll just buy an entire new/refurb. alternator instead
(the regulator is usually located inside the alternator).
/EDIT
Cheers
Note that if the shop claims no problem, it could be a flakey thing -- where the regulator works until it hits a certain temperature or load, and then just shorts out and blows the (sensitive) halogen lamps.
An empeg would be safe, though, as it is tolerant of higher voltages (to a point).
Cheers
Posted by: larry818
Re: Low beams keep burning out. - 02/12/2007 13:38
Quote:
If it were that, then high-beams wouldn't work either. But they do work.
For whatever reason, the high beams are fused and lows are on a breaker.
I'll try and find a schematic on this...
I thought it was telling that the low beams burn out together... and don't look burned out when removed.
Monitoring the voltage would be useful.
Are you getting all the replacement bulbs at the same source?
Posted by: larry818
Re: Low beams keep burning out. - 02/12/2007 13:49
Quote:
I'll try and find a schematic on this...
I didn't find anything linkable. My '81 malibu was this way, but I did find a schematic for an '87 that was just fused.
It should be a simple thing to measure the voltage at the low beams when they are not working...
Posted by: mlord
Re: Low beams keep burning out. - 02/12/2007 14:16
Quote:
- Bulbs are halogens. They are the kind where you have both the low and the high beam contained within the same actual bulb itself. When you look at the bulbs in a cursory fashion, they don't look particularly bad. But when you look very close, you can see the difference between the highbeam filament which looks fine, and the low beam filament which looks blobby and slightly melty (but not blackend per se).
Tony, dig out an ohm metre and check for continuity across the low beam filament.
(can one do this with halogen bulbs?)
If it's really burned out, there shouldn't be any conductance there at all.
-ml
Posted by: larry818
Re: Low beams keep burning out. - 02/12/2007 14:26
Quote:
Tony, dig out an ohm metre and check for continuity across the low beam filament.
(can one do this with halogen bulbs?)
Yes, halogens are just incandescent bulbs filled with a halogen gas rather than argon.
http://en.wikipedia.org/wiki/Halogen_bulb
You're probably thinking of the HID lights.
Posted by: pca
Re: Low beams keep burning out. - 02/12/2007 14:43
A couple of thoughts occur.
1) Vibration in conjunction with bad contacts. I had a car where the spring clamp mechanism that holds the base of the bulb (which is the earth) in place was worn and weak. The result was that when you drove the car, especially if you went over a bump, the bulb would bounce in the socket and momentarily flicker. After a remarkably short time, the
low beam filament would burn out! It never affected the high beam. I put it down to current spikes combined with the vibration mechanically stressing the thinner filament.
2) One or more faulty diodes in the alternator. Alternators are three-phase AC generators, diode rectified to a not particularly clean DC. If one of the diodes goes out, you will get a fairly high voltage AC signal superimposed on the the nominally 12V DC line. A scope will show it instantly, a meter set to AC may well show it as an AC component to the DC voltage. If you can measure frequency with the meter, you'll see it change with engine RPM.
As Mark says, if the voltage regulator in the alternator was bad you may well also get more than 12-15v out. This would make the current going through a specific resistance, ie. a bulb, increase proportionately. The high beam filament may be man enough to take it, the low beam probably wouldn't. However, I suspect you'd also have all sorts of problems with other things working oddly/not working/smoking as well. Such as tail light bulbs, interior lights, etc. Note that a bad diode in the alternator would kill the regulator fairly fast as well, so we might both be right
At least in the UK, the regulator and diode pack are integrated into the alternator. It's easier and cheaper to replace the whole thing. If it is a bad alternator, eventually it will eat the battery as well.
pca
Posted by: wfaulk
Re: Low beams keep burning out. - 02/12/2007 16:29
I would say that the obvious first step would be to check the voltages at the headlight receptacles. Both low beam and high beam with the car set to low beam and high beam and during the change in each direction. While you're there, you might want to make sure there's not a short in the connectors, so try measuring impedance between the high and low beam contacts with the power off.
Posted by: mlord
Re: Low beams keep burning out. - 02/12/2007 16:37
Quote:
I would say that the obvious first step would be to check the voltages at the headlight receptacles.
I suspect that may be somewhat tricky to achieve at 55MPH. 
But the lighter socket inside the cabin should show pretty much the same voltage as anywhere else.
Cheers
Posted by: tfabris
Re: Low beams keep burning out. - 02/12/2007 17:47
Quote:
For whatever reason, the high beams are fused and lows are on a breaker.
VERY interesting.
These are all good suggestions here, I'm going to try the things you're mentioning. Thanks, everyone, I'll report back.
Posted by: lastdan
Re: Low beams keep burning out. - 02/12/2007 17:52
if the bulb is really burned out, over voltage is the most likely cause.
no fuse wrong or faulty will cause this.
a short that causes another consumer to pull power through the bulbs, making the bulbs act as fuses is possible, but not very likely at all.
if the cause is over voltage, the regulator may not be at fault, but should be suspect.
the test-
with engine off, switch on lamps to make sure they're still working.
connect volt meter to bulbs (either side, but use the ground point at the bulbs for meter hook up), you should see something like 11.x volts with the bulbs on and the engine off.
start engine and rev to ~2,000 rpm.
load the electrical system by switching on things like the A/C, power windows, sound system, anything that requires a fair amount of juice.
I expect your charging system to operate within 13.2 - 13.8 volts. pushing 15 volts is not cool. in fact, at 15 volts I would say you have a problem.
if you do find higher than comfortable voltage start checking --
-voltage drop from alternator case to ground points at 1)battery negative post, 2)bare metal of engine and 3)any gang connection on the frame. half a volt (1/2) is the highest you wanna see in any case.
-as silly as it may sound, really make sure your battery connections are perfect (1/10 drop while cranking motor)
-if the alternator is mounted to the engine via vibration dampners, check the hell out of the alternator-to-engine ground strap. twice.
-check the smaller wires connected to the alternator, you should see a black plug on the rear/side of the alternator. with the engine off, remove this connector and make sure it's in good shape. a poor connection here will trick the regulator into an over charging state.
if you do find higher than normal voltage, the regulator may be the fault, but keep in mind that it's not that hard to trick a regulator into thinking it needs to go mad on the field winding in order to do its job.
there should be no more than 1/2 volt drop from the large lead on the back of the alternator (B+) to the center of the positive post on the battery with the engine running a good load on the system.
this all assumes the bulbs are realy burning out. the fact that they seem to die at the exact same time (left and right) is a little odd.but lets assume you know power is present at the bulbs when they're not working. (both the positive and negative side)
in 20 years of working on cars full time, over voltage is the only cause I have ever witnessed myself.
a few thoughts-
use 'Osram' bulbs, and never touch the glass to anything, including your fingers.
do not use high wattage bulbs (45-55 watts is normal)
make sure there is no after market alarm or fog lamps that may be wired in.
Posted by: larry818
Re: Low beams keep burning out. - 02/12/2007 22:14
Quote:
I suspect that may be somewhat tricky to achieve at 55MPH.
I guess I should have been more clear. Assuming the bulbs are still out when stopped, check to see if there's any voltage at all. That would indicate if something is amiss with the breaker (if any).
But yeah, the cig lighter port would tell you if you're over voltage at speed.
Posted by: larry818
Re: Low beams keep burning out. - 02/12/2007 22:18
Quote:
use 'Osram' bulbs
I wanted to mention this too. At one time I got a few cheap chinese bulbs that would only last a couple of weeks. The Osrams live forever.
Quote:
do not use high wattage bulbs (45-55 watts is normal)
Thanks to the HID lights others are sporting, I've got 100/140 watt halogens in my car, just so I can maybe see what I'm about to hit...
Stock wiring is holding up to it.
Posted by: AndrewT
Re: Low beams keep burning out. - 02/12/2007 22:31
Quote:
use 'Osram' bulbs
I researched this a couple of years ago and Osram Silverstar quartz halogen were highly rated. I didn't notice any drastic difference when I fitted some myself though. Be warned though, some websites offering these bulbs use HID 'after' photos.
Quote:
Thanks to the HID lights others are sporting, I've got 100/140 watt halogens in my car, just so I can maybe see what I'm about to hit...
Don't be left in the dark, you can get HID conversion kits fairly cheaply nowadays. I've been using an H7 bulb replacement kit on dip beam for 18 months now (bought from eBay/HK) and I wouldn't go back. Local legislations may prohibit this where you live, and I've also seen a lot of naysayers scaremonger folks away from installing these kits - check with your vehicle testing station. I made a point of mentioning the upgrade at my car's annual vehicle test (MOT) and the tester didn't have any objections.
Posted by: larry818
Re: Low beams keep burning out. - 02/12/2007 22:44
Quote:
Don't be left in the dark, you can get HID conversion kits fairly cheaply nowadays. I've been using an H7 bulb replacement kit on dip beam for 18 months now (bought from eBay/HK) and I wouldn't go back. Local legislations may prohibit this where you live, and I've also seen a lot of naysayers scaremonger folks away from installing these kits - check with your vehicle testing station. I made a point of mentioning the upgrade at my car's annual vehicle test (MOT) and the tester didn't have any objections.
Thankfully there's no inspection here (although there should be everywhere), so no trouble that way.
Unfortunately, my car has the dual beam bulbs, and there's a real lack of good info on dual beam HID lights. Most offer bulbs that don't move, so you lose high beam. Others it seem one can't be sure of what you're getting...
I did convert from the 2004 light to H4, so it seems converting to HID *should* be easy...
Posted by: mlord
Re: Low beams keep burning out. - 03/12/2007 01:19
Quote:
Thanks to the HID lights others are sporting, I've got 100/140 watt halogens in my car, just so I can maybe see what I'm about to hit..
What's HID ?
EDIT: Never mind..
Posted by: gbeer
Re: Low beams keep burning out. - 03/12/2007 01:56
Posted by: tfabris
Re: Low beams keep burning out. - 03/12/2007 04:07
Thanks, Gbeer, those are useful schematics.
Posted by: tfabris
Re: Low beams keep burning out. - 04/12/2007 14:45
Although recent
tricky weather in the area has kept us from going outside to work on the car, I do have updated diagnostic information:
- The car's turn signals have recently been known to blink slowly. This is intermittent.
- The power windows have been known to go up and down slowly. This is also intermittent.
Combined with the other reported symptoms, what does this indicate? Voltage regulator?
Posted by: tfabris
Re: Low beams keep burning out. - 05/12/2007 04:49
Quote:
Also, connect a volt meter to the headlight socket and rev the motor. I'll bet the volts don't go over 15, but if they do, then it's the voltage regulator.
Motor off: 12 volts.
Motor starting: 15 volts, peaking slightly higher, like 15.2 or so.
Motor idling: 14.5 volts.
Motor revving: 14.7 volts.
Does that mean anything bad, or does it mean a normally operating vehicle?
All of the above was with vehicle working normally on all axes. For instance, the turn signals worked at normal speed.
Oddly, the lights are working right now. When we moved the car the other night and the lights didn't work, we *assumed* they'd burned out again, but they don't seem to have done so. It was a very cold day, and snowing, maybe that was a factor.
Do any of these data points help?
Posted by: lastdan
Re: Low beams keep burning out. - 05/12/2007 06:22
Quote:
Do any of these data points help?
yes.
I think we can all agree the bulbs are not failing (:
http://gkb.servehttp.com/images/achevia/sch2.gif
as this image shows, both positive and ground are switched.
it would really be a good idea to find out which goes missing.
that's easy to do at the bulb.
does that car have Day Running Lights?
when the lows fail, what happens when you switch the main switch off?
seems like there's a good chance the breaker is just doing it's thing, maybe it's too sensitive, or maybe it's functioning as it should, protecting the circuit. but before you even bark up that tree, you should verify that power goes missing at the bulb on the hot side, if that's the case check to see if power is going in and out of the breaker. seems like you could just bypass it with a 20 amp fuse.
I would expect slightly lower voltage readings from your test, but if it's really cold and the test was done soon after starting the engine, it's not that far off.
Posted by: larry818
Re: Low beams keep burning out. - 05/12/2007 10:25
Yes, these data points indicate that the charging system is fine.
Motor starting should have been 10 or 11 volts, but no biggie.
Since the lights are resetting, it's gotta be an automatic breaker somewhere.
Here is what it should look like:
http://www.aquavolt.com.au/persistent/catalogue_images/categories_thumb/225010.jpgHunt it down and replace.
The slow blinkers / windows is probably an unrelated problem.
And we americans have the nerve to call Lucas the prince of darkness...
Posted by: tfabris
Re: Low beams keep burning out. - 05/12/2007 19:33
Quote:
I think we can all agree the bulbs are not failing (:
Well, actually, they definitely are failing, at a much higher rate than they otherwise should, it's just that this *last* time they hadn't actually failed.
Quote:
does that car have Day Running Lights?
No.
Quote:
when the lows fail, what happens when you switch the main switch off?
Define "Main Switch". Do you mean the main headlight on/off switch? And what do you mean "What happens"? Well all the lights on the car turn off like they're supposed to. What else would you expect to happen?
Quote:
seems like there's a good chance the breaker is just doing it's thing, maybe it's too sensitive, or maybe it's functioning as it should, protecting the circuit.
I'm thinking the same thing.
Doug Burnside wanted to post here with a detailed reasoning of something, but the BBS ate his post again. But he thinks there's an "open" in the hibeam/lobeam switch that is triggering that circuit breaker.
This gels with an additional statement Vixy has made (oh hey, I mentioned it earlier in the thread): Sometimes she thinks the *act* of using the hibeams is the thing that makes the lobeams fail. This didn't make any sense to me until now. But in theory, a short in the hi/low switch could easily cause that circuit breaker to pop, couldn't it?
I think our next course of action is to replace the hibeam/lobeam switch as Doug suggested.
Everyone concur?
My only concern: How much trouble is this, and does it involve working around the airbag? Is this something I can do in an evening?
Posted by: Robotic
Re: Low beams keep burning out. - 05/12/2007 20:19
Quote:
Define "Main Switch". Do you mean the main headlight on/off switch? And what do you mean "What happens"? Well all the lights on the car turn off like they're supposed to. What else would you expect to happen?
For the case where the car *did* have daytime running lights, there is a switch (just like all cars) that turn on the headlight circuit. This also lights the dash and marker lights.
Hope you get things sorted out! 
Posted by: lastdan
Re: Low beams keep burning out. - 05/12/2007 20:57
>>Everyone concur?<<
with all due respect, I do not.
while it may well be the case, it may well not be.
I did mean the standard head lamp switch, and asked about the DRLs because it can help narrow things down. the DRLs work when the switch is off, so had they come on when you switched them off we would have known more about the power path... but if the car doesn't have them, it doesn't matter.
maybe I've become confused, but did you say the the first sets of bulbs that didn't work were confirmed to have 'blown out'?
working with the air bag is not that hard. to be safe, disconnect the battery first, and then make sure everything is plugged in before you hook it back up, this way it should not log any trouble codes in the SRS (airbag system).
I would bypass the breaker with a standard fuse, 20 amp.
if it snaps, you can always hook the breaker up again, but at least you have a record that a short/high load did occur.
the next time you catch them not working, unplug both bulbs and check for power at either one (tan wire at bulb for low beam).
if power is there, plug one bulb back in and check again.
if the reading drops out, check voltage drop across the switch and the breaker.
I just printed out the diagram for the "SC" model and it looks nothing like the diagram posted above. what variant is that car?
>>Well, actually, they definitely are failing, at a much higher rate than they otherwise should, it's just that this *last* time they hadn't actually failed.<<
this is the part that confuses me.
if the bulbs are actually cooking, it's not an issue with any breaker, switch, or short. you just can't kill bulbs that way.
Posted by: AndrewT
Re: Low beams keep burning out. - 05/12/2007 22:09
I can't help but think that the bulb filaments are failing because either:
a) They are burning out due to an overvoltage situation.
- or -
b) An intermittent connection is [thermally] stressing them.
For a) I'm still unconvinced that we've been able to rule out an intermittent voltage regulator at the alternator. I'd imagine the increased brightness of the lamps would probably go unnoticed while driving on busy roads with streetlighting. The dashboard lights might give a clue but OTOH, they are quite likely to be PWM driven and therefore less susceptible to voltage fluctuations.
Have you had an OBD [etc] diagnostic reading taken? Taken from
here, there are a number of helpful fault codes that the ECU might have snagged:
Code:
P0560 System Voltage Malfunction
P0561 System Voltage Unstable
P0563 System Voltage High
Some ECUs reset the stored fault codes after a number of ignition cycles and others keep then in a pseudo FIFO buffer where new codes displace old ones. Depending upon how yours works you may have 12yr old codes stored so you will need to get the codes read/reset, go away and blow some bulbs then return for a fresh reading.
I also have another hypothetical scenario: Lets say there is something inductive on the car's 12v supply, e.g. a suppressor choke, wiper motor or a blower motor. If there's a faulty (intermittent) feed to that inductor, when the power breaks there will be a back EMF when the magnetic field collapses around the inductor that will send a negative spike back onto the 12v supply.
I appreciate this theory sounds a bit far fetched.
I just wanted to get you thinking about (or looking for) things like big suppressor chokes, perhaps aftermarket ones the previous owner fitted to prevent 'thumps' killing speakers when the headlamps (etc) were switched on?
Posted by: mlord
Re: Low beams keep burning out. - 06/12/2007 01:44
Quote:
Oddly, the lights are working right now. When we moved the car the other night and the lights didn't work, we *assumed* they'd burned out again, but they don't seem to have done so. It was a very cold day, and snowing, maybe that was a factor.
Really, Tony, the only data point that matters much here is, are the bulbs *actually* really burned out? Check for continuity through the filament (ohmmetre or similar).
Without knowing that for sure, this is impossible to correctly diagnose.
If they are burned out, then it's overvoltage.
-ml
Posted by: gbeer
Re: Low beams keep burning out. - 06/12/2007 02:46
Over voltage? in a car? Could the spark from the ignition coil blow a filament?
Posted by: music
Re: Low beams keep burning out. - 06/12/2007 15:31
Quote:
Over voltage? in a car? Could the spark from the ignition coil blow a filament?
I think he is referring to overvoltage from the charging system. I.e., alternator/regulator. Not the ignition system.
Posted by: Neutrino
Re: Low beams keep burning out. - 06/12/2007 22:43
Don't know if you've solved this or not Tony but an interesting little circuit. The only three points I see that would only effect both low beams are the dimmer switch, the point at which the low beam wire connects to the dimmer switch and what looks like a connector in the low beam wire after the grommet. Have you tried just rapidly toggling the low beam dimmer switch when this happens? I thought it interesting that the right lamps are back fed to provide 6 volts to both headlights for DRL's. Pretty crafty and cheap to do.
Posted by: tfabris
Re: Low beams keep burning out. - 07/12/2007 05:28
This is interesting to know about that circuit. That's the kind of information I'm looking for.
One thing though. This car is not equipped with DRLs. So are we sure we're looking at the right schematic?
If I knew where that "connector at the grommet" was geographically, that'd be real nice. That's something I could easily check if I only knew where the connector was.
Posted by: lastdan
Re: Low beams keep burning out. - 07/12/2007 15:52
http://farm3.static.flickr.com/2404/2093849776_af98968550_b.jpghere's another diagram.
allegedly for a 1995 Achieva SC w/o DRL.
Posted by: tfabris
Re: Low beams keep burning out. - 07/12/2007 16:54
Interesting. Am I reading it wrong, or does that diagram have no fuses or circuit breakers on it?
Posted by: larry818
Re: Low beams keep burning out. - 07/12/2007 17:03
Quote:
Interesting. Am I reading it wrong, or does that diagram have no fuses or circuit breakers on it?
There are some fuses on it, just not associated with the headlights.
This is not a complete schematic. The fuses would be upstream of the switch in the upper left corner.
Posted by: tfabris
Re: Low beams keep burning out. - 07/12/2007 18:03
What about that (alleged) timed-reset circuit breaker that only exists for the low beams?
Posted by: Neutrino
Re: Low beams keep burning out. - 07/12/2007 20:05
It sounds like that schematic is not what you got. I would imagine that your car has a close variant though. The grommet is where the wire runs through the firewall into the engine compartment. The connector can be anywhere from there the where the wire splits off the go to both head lights. If this is indeed indicative of your wiring and you have determined that the lamps are not actually failing, you might try toggling the dimmer switch rapidly when this happen to see if the lights come back on indicating that the problem is in the switch or opening the hood and basically just shaking the wiring looms in the engine compartment to see if the lights come back on pointing to a bad connection there somewhere. I think it is unlikely that you would have simultaneous lamp failure. It is far more likely that you have a bad switch. Again, if your wiring is similar to this.
Posted by: tfabris
Re: Low beams keep burning out. - 07/12/2007 20:21
This sounds like the most logical explanation to me.
Posted by: gbeer
Re: Low beams keep burning out. - 08/12/2007 00:59
Posted by: Neutrino
Re: Low beams keep burning out. - 08/12/2007 06:00
Wow! Another nice schematic! It looks like the switch is still the most likely suspect. This one shows a 20 amp circuit breaker but it supplies power for both the high and low beams. I thing I notice is that the flash to pass switch fires up the high beams while allowing the low beams to stay on too! Now that's got to be bright!
Posted by: FireFox31
Re: Low beams keep burning out. - 08/12/2007 14:18
Tony, even though you've got some good replies, why not call the Car Talk guys anyway. Stump The Chumps!!! Hahaha.
Posted by: tfabris
Re: Low beams keep burning out. - 08/12/2007 17:50
Wow! Another nice schematic! It looks like the switch is still the most likely suspect.
I was going to say the same thing last night, but they brought the board down while I was mid-post. :-)
Posted by: gbeer
Re: Low beams keep burning out. - 08/12/2007 18:13
The switch, or there is a dead short on the low beam circuit somewhere between the switch and the bulb.
If it's a short the breaker should reset after having time to cool.
You could unplug a HL and jumper from the battery to each terminal to see that the bulbs light.
Or better yet, with the lights off, unplug the head lamps and check, with an ohm meter, between the terminals of the harness and ground. If you get continuity where there shouldn't be, it's a short, otherwise it's gotta be the switch or a bad breaker. Breakers do fail sometimes.
Posted by: Neutrino
Re: Low beams keep burning out. - 08/12/2007 20:48
It could be a short, if it is, then the HB's won't work either until the breaker resets unless you use then passing switch, then they should work.
Posted by: tfabris
Re: Low beams keep burning out. - 09/12/2007 06:15
It could be a short, if it is, then the HB's won't work either until the breaker resets unless you use then passing switch, then they should work.
That's great information. I'm pretty sure the high beams work even when the lows are out. But I'm not certain of this. The trick with the passing switch is a good one... Strange they'd design it so that flash-to-pass would override the breaker?
Posted by: Neutrino
Re: Low beams keep burning out. - 09/12/2007 16:04
The flash to pass is on it's own fuse. when used it is the only time that both the low beams and the high beams are on at the same time. At 50w / lamp thats 200watts @ 12 volts. Very close to the rating of the breaker.