The drain pump shorted out, a common problem on this model. Replaced that.
The short blew the ACST (a kind of a switch) on the main board, a common problem on this model. Replaced that.
The damage was more extensive on main board than I’d hoped, an additional relay is probably bad and an unknown number of other components. Replaced that.
The new main board fails to communicate with the inverter board, a common problem on this model.
I’m going to borrow a DMM to troubleshoot, but at this point I’m stuck between dumping more money into it, or returning both the new main board and the drain pump which have not seen action yet, and just buying a new washer.
Blegh I wasn’t gonna share this earlier since it still stings but:
I just went through it with my 1994 K1500 truck. Head gasket leak fouled every single damn one of the sensors the oddball and short lived Throttle Body Injection system ECU relies on. All of them, I soon discovered. First it was only rough running when cold, then became undriveable. Plus it leaked coolant out the rear before it worsened and got into the oil, so it evaporated into the distributor and MAP sensor for months probably and corroded them into a nice bright green copper oxide.
One part at a time scouring old forums and watching pixelated old YouTube repair guide videos for advice on why it was running rough after getting the gasket done, especially cold. Eventually got it…$1900 later. Even did the fuel pump. This particular truck model year is worthless even operational so I was definitely weighing my options before that last magical part swap lol.
Didn’t take many pics but here’s one of the distributor:
Ugh, pre-OBDII EFI. I’ve got a '94 4Runner that’s been sitting because it doesn’t run right, my usual mechanic just flat-out refuses to service it (because no ODBII), and I can’t muster the motivation to dig into it myself.