Went on a beer run last night and left light shut down half way to the store. This morning light still did not function so I went through the system. All wiring solid. The ballast was not bolted in it’s place, but that wasn’t an issue, just my frustration with body shop. I had an identical new ballast that I had from AlphaHID (now defunct). Plugged in and it works. Swapped back and forth 3 times. Every time: old no works, new works.
When I disconnected the OEM left (drivers) side headlight harness from the ballast, neither headlight would function. So while I have not looked at the wiring diagram and have not thought this through, I believe that the shorting ballast may have been the entire system on/off issue despite the switch being off. At least that’s what I’m hoping. That mystery ghost activation hasn’t occurred again. I did put in a new battery as well...another variable.
2000 Toyota MR2 Spyder, 2020 Mazda 3 Hatchback 6MT
As I originally mentioned aftermarket electronics are always suspect when you have bizarre electrical behavior. Toyota does electronics right, there modules, ECUs and wiring almost never fail. European cars on the other hand, everything is suspect because of poor architecture.
This is why I frown on those that want to add all kinds of aftermarket accessories which if not done right end up being the source of gremlins that is hard to pinpoint.
Nice that you were able to find the source.