Lj78 All dash lights stay on when running. (1 Viewer)

[RMessmer]

I'm trying to sell my Lj78 but I would very much like to fix this electrical issue before I list it. All dash lights including battery, filter, etc. (excluding check engine light, strangely) stay on when the truck is running. I replaced the alternator about 5 years ago but I wasn't sure if it was the highest quality part so this week I replaced it again with a used factory alt from EBI Cruisers that they said was good. Didn't fix the problem. I cleaned the connection at the alternator, checked the batteries, cleaned the grounds next to the fuse panel under the dash, and checked the connections behind the gauge cluster.

Anyone have any other suggestions before I lose my mind and buy this truck it's 4th alternator in the time that I've owned it?

/Anyone in Washington state want a really nice white Lj78 with only a few minor electrical gremlins?

 

[coldtaco]

Go to a car parts store and have them do a test of the alternator?

 

[snowyhermit]

I'm not sure I'd suspect the alternator at this point. Especially if you don't have problems with batteries dying. By the 90s, there may be a computer responsible for the lights. Probably a separate one from the one from the one that controls the check engine light, so you may not be able to read codes to diagnose the issue. Either that or an "annunciator test" circuit somewhere with a stuck delay. I think even pre-computer instrument clusters typically test all the warning lights on start up, so it must be a stuck relay or shorted diodes or something like that.

I wasn't able to find schematics, but if you have the FSM that may help

 

[Rigster]

Does this have a separate voltage regulator? I would imagine it is built into the alternator by this vintage, but I am not as familiar with the Prado's. I would verify this as a starting point since you are pretty sure the alternator is good.

Otherwise the multiple light scenarios in my experience has been a poor ground somewhere. As a test, you could carefully add a ground from the cluster to a known good ground to see if that makes the lights go out. If it does, then you need to inspect the current factory wiring from the cluster back - looking for the culprit. Best of luck on this electrical gremlin!