I went to buy a second empeg/riocar unit today. I have my first empeg MKII with 2.0 installed and operational in my car. The new unit I was about to buy was a Riocar MKIIa with 3.0a installed. I tried plugging the new MKIIa to my existing sled to see if it worked. However, the unit failed to display any sign of life. No light, no booting, nothing. I then went through the trouble of swapping my sled with the sled that comes with the Riocar. That way the unit booted. Naturally I plugged in both sleds to the very same ISO power connector.

What could be the problem? I thought the sleds were supposed to be identical. Could the 3.0a software cause the unit not to look alive at all?

You've been FAQ'ed.

Check your fuses. Especially the one inline on the yellow wire on the sled harness.

Could the 3.0a software cause the unit not to look alive at all?

If it's not booting then no software is being run, so no.

Check you old sled very carefully. It's possible that one of the connector wires separated at an inopportune moment.