I've been tinkering with the dashlight dimmer switch today, as it never worked in my car. The dash lights would always be full bright 100% of the time. I took it out and tested the connector for continuity and voltage, per the manual. Everything checks out perfect. Figuring it was the controller itself, I took it apart and reflowed all the solder joints. No effect. Then I went out and got another one from the salvage yard. Still no effect.

Aren't the dash lights supposed to go out completely when the controller is disconnected, though? I've got the thing completely removed, yet the dash lights come on full bright if I turn them on. I'm starting to think someone bypassed the dimmer and connected RED to BLK further up the loom or something.

Anybody have any insight on this?

 

Could be.

If you remove fuse 19, do the lights turn off.

 

Yea, removing fuse 19 turns them off (in addition to the parking lights and license plate lights). I'm going to guess the next step is to trace the RED, BLK, and RED/BLK wires from the dimmer down to the fuse box and keep an eye out for signs of modification or grounding?

 

Have you carefully inspected the dimmer switch plug? That's where most people short the red wire to the black wire.

 

I just checked it pretty closely and didn't see any signs of modification or damage.

 

It's possible that the red wire is damaged and shorting to ground rather than due to a red-black wire splice job.

 

Yea, I'm thinking now it's got to be one or the other. I'm disassembling the dashboard as we speak so I can get a better look at the wiring.

 

Well I'm a bit stumped. I traced the RED wire from the dimmer switch connector back towards the dash fusebox. Everything looked stock and unmodified. I discovered there was a split in the RED wire. One end led to a large connector in the fusebox. The other leads to a larger wire bundle that disappears behind the steering column.

I tested for continuity between RED and ground at the splitting point and at the fusebox connector. There was continuity at both those locations. The splitting point was securely insulated with electrical tape and part of an insulated wire bundle before I unwrapped it.

I'm guessing if RED is shorted to ground, it's further up the bundle, somewhere between the split point and the under hood fusebox? Perhaps near the combination light switch?

Does it sound like I'm even on the right track?

I've attached a pic showing what I see...

 

Yep

If you disconnect the split crimp connector to separate the three red wires, which red wire has continuity to body ground? That's the wire that is creating the problem.

 

It's the one leading up behind the steering column. Does that wire lead to the base of the combination light switch lever? I can't see that bundle after it disappears behind the steering column.

 

Hmm... as it turns out, it's not just the section of RED wire that leads behind the steering column to the Dashboard Wire Harness that has continuity to body ground. The section of RED wire that leads directly from the fuse box connector is also grounded! That same RED wire leading from the fuse box has battery voltage when the dash lights are on.

Also, the RED/BLK wire has continuity to body ground as well. The RED/BLK wire does get normal battery voltage when the dash lights are switched on. Something else peculiar about the RED/BLK wire is that it terminates into a large connector plug (along with a lot of other wires) and then apparently continues on to the large green connector at the dash fuse box.

I'm a bit confused. How or why would both the RED and RED/BLK wires be getting continuity to body ground (the RED one seemingly from two different sources)? I've yet to find any sign of damage on either wire. Common sense dictates that the only wire leading off the Dashlight Brightness dimmer that should be grounded is the BLK wire. Am I wrong about this?

Here's a circuit diagram straight from the service manual if anybody can shed some more light (or hopefully less hehe) on this.

 

I finally figured this out... and lol wow! For ***** and giggles I tried disconnecting body ground connection G501 from under the steering hanger. It worked! The Dashlight Brightness Controller works like it's supposed to. The problem is that, according to the service manual, body ground G501 is ONLY supposed to ground out the car stereo. After disconnecting G501 the car stereo still works! Who the hell knows where the stereo (which is some aftermarket Pioneer stereo btw) is actually grounded now. As an added bonus, if G501 is disconnected, the stereo only works when the gauge lights are on and when the dimmer dial is more than halfway up. I think I can see the black ground wire near G501 that was modified, but I have to pull the entire dash off to access it. Whoever installed this stereo years and years ago was a moron, clearly. Whatever, it sucks anyway and only works about half the time. If and when I decide to buy a new stereo, I'll definitely be installing and wiring the thing correctly.

 

Sounds like fixing the radio wiring will solve all of your problems.

The stock radio gets voltage for illumination on the Red/Blk wire from fuse 19. However, if this wire were grounded, fuse 19 would just blow.

The previous owner probably mistakenly used the Red wire from the dimmer circuit to power the radio. Remove the radio and look for a solid red wire spliced into the connector. Also look for the Red/Blk wire, which seems to be disconnected.

The two wires that instead should power the radio are Yel/Red from 15A dash fuse 23 (ignition switch power) and Wht/Blu from the 7.5A hood Back Up fuse (constant power for memory).

 

I finally got it fixed! I got fed up and dropped the steering wheel and pulled off the entire dashboard earlier today. I know exactly what happened now, and it was rather boneheaded on the previous owner's part. Their dashlight brightness dimmer went out and rather than simply jump RED to BLK at the dimmer connector, they took the entire instrument panel out and jumped the RED wire for the instrument panel circuit to the nearest ground wire, which happened to be the G501 stereo ground connection. They also did a rather sloppy job of it (see the pics below, you might lol).

I ended up removing their horrible splice/twist/electrical tape job and then braided, soldered and shrink tubed the RED instrument panel wire back together. Then I insulated the open in the G501 wire they made and put the dash back on. Everything works perfect now, even the aftermarket stereo. Before, the stereo would cut out randomly if you touched the buttons or volume dial. Hasn't done that once since the fix. A lot of work just to get the dashlight brightness controller to work, but hey... it was bothering me. No retreat!