Hello all longtime lurker, first time poster. I am attempting to diagnose this odd issue an owner brought to us. He complained that his panel would not press to test or dim and the only two working lights were gear up/down. No input would trigger a corresponding light to ignite. Upon checking, I found full bus power and ground supplied to the panel. Thinking the panel was likely at fault we sent it off to International Avionics where it tested healthy. Once I reinstalled the panel I discovered that when switched to emergency bus(it has a standby alt), the annunciator functioned properly, tested all lights including master warning, and dimmed as it should. It should be noted that in this configuration I had the same bus voltage supplied to the panel. It may be coincidental but something else I discovered recently was the supply lead coming from the alternator had been abraded where it passes through the engine baffling and must have briefly shorted. Any thoughts or ideas would be appreciated.