I realize electrical issues on a vehicle can be hard to narrow down, but here's hoping some direction can be provided on where to look. I am an engineer and experienced troubleshooting electrical issues, as long as I have good information and schematics to follow.

Our 2006 Expedition recently experienced numerous anomalies that seem unrelated but could be tied together somehow. First, the rear hatch window unlatches whenever the A/C is turned on. The headlights in the Auto position will also turn on, even in daylight, when the A/C is turned on.

Attempts to lock the doors via the door lock switch or the key fob also causes the rear hatch window to unlatch.

The A/C blower will not increase its speed through the four speed selections, and switch to the fourth (highest) speed causes the engine to shut down. I understand this might be a power saving feature the engine computer invokes if it senses an issue in the vehicle.

When these issues first occurred I contacted a supplier of reconditioned engine computers, one I had success with on replacing a computer on my 2006 F150 in 2018 (still running great). I ordered a new computer, installed it and the vehicle behaved normally for almost five (5) weeks, and then all the same issues returned.

I contacted the computer supplier and had another one sent to me under warranty. I just installed it and the issues remain.

I am wondering if is there a way to isolate certain circuits, one by one, and see if one of those circuits might have a bad wire. For example, maybe the rear hatch window latch or door sensor is causing the issue and is affecting other circuits related to the A/C, headlights and door locks. Or one of those other circuits causing the issue. I'm thinking of pulling fuses for those circuits one by one to see if doing so might reveal something.

The issues I am having seem too varied to offer one specific solution, given that I have already tried two different engine computers, but some general tips on electrical troubleshooting would be much appreciated.

Thank you all...