Dome light and tach on '92 Explorer

[logeorge]

The dome lights on my '92 Explorer got to where they wouldn't come on by opening the doors or tailgate, but would work by turning the headlight switch. Now they won't work at all. I checked the bulb and fuse. They were OK. Replaced the headlight switch with no results. Any suggestions? The tachometer started going to about 3300rpm with the ignition switch turned to "run", even before starting the engine. At first it was intermittent, now it's all the time. I don't think the two problems are related, but automotive electricity is not something I'm good at or experienced with. Any help would be appreciated. I don't have any wiring diagrams for this vehicle. Tried to find one on the internet without success.

 

[jmdirk]

If you've got a volt meter, you can check for voltage at the bulb. The other issue could be the ground for the dome light. It's grounded direct to it's bracket and then screwed into the roof, there is not ground running back to the switch.

Not sure they are related either, there doesn't appear to be any common circuits or even connectors between the dome lamps and the tach. Though the tach signal does share a ground with the glove box lamp. Tach signal is basically connected to the PCM, ICM and the data link connector.

 

[logeorge]

Tach Is working! No idea how long it will last, but it's working now. I found a couple of videos on how to repair the tach in an F-150 truck. The principle is the same. You have to dismantle the instrument cluster and unplug the tach ( carefully so you don't crack the plastic piece behind the face). Looking a the circuit board on the back of the guage, with the top up, you will see 4 or 5 soldered connections on the upper left that look corroded compared to the rest of the soldered joints. The board will likely show signs of overheating in that area. With a small soldering iron, carefully re-melt the solder on these connections so contact is re-established with the components on the other side of the board. I cleaned mine with denatured alcohol first. Re-assemble and check for operation. I should have taken the names of the videos so I could have put them in this reply, but an internet search should locate them. Still haven't figured out the dome lights, though! L. O. G.