Need help on bulkhead wiring

Dart, we have the manuals and I have been working with my son to trace the yellow wire back to see where he loses the voltage. He isn't extremely mechanically savvy but is putting forth the effort nonetheless. he got the bulkhead connector apart and cleaned it up but still no joy yet. I'll pick it back up tomorrow with him and have him start under the dash and work back towards the ignition switch, that is what I am suspecting at this point. If it is the switch, they are cheap enough but not sure he could change it.

Anyone in the San Diego area looking to tinker on their holiday weekend?