No dash lights with key on
 

I'm hoping for some hopefully quick help. I haven't noticed this because I haven't driven the car at night since I overhauled the interior which included a new dash harness.

If the key is in the acc or off position and you turn the lights on, I have dash lights and everything works.

As soon as you turn the key to the run position (including after starting the car) I no longer have dash lights. I do however retain the cabin lighting features like the HVAC and shift position back lighting.

I was planning on taking the car to a meet tonight, but that's a bit in jeopardy now if I can't figure out this dash lighting issue.

Does anyone have any ideas on this?

Still working on this with a little update.

The lights aren't completely out when the key is in the on position. They are nearly imperceptibly on when the engine isn't running but the key is in run position. They are about 40-50% brightness when the engine is running. During this situation you can see the indicator lights functioning, however headlight functionality, brake lights, hazards and indicators front and rear do operate externally.

dash lights
 

did you try turning the light switch? Maybe a ground? Good luck
Tim

Yes. the dash has led bulbs in it which do not respond to the rheostat, so they only function when the switch is at about the top 5% of rotation. But that's certainly the first thing I checked off the troubleshooting list.

dash lights
 

I figured that you did,but you never know.Sometimes it can be the littlest thing.Where they working before and have you done any work recently?If they were try looking where you were working for a loose or broken wire.
Tim

Sounds like the dash harness has some crossed wires. Perhaps the grey rheo wire is being used as a ground by something engaged in the run position on the ignition switch.

Could also be an issue with the turnsignal switch (did you replace it during the resto of the dash area?), later NOS units have different connectors and perhaps that is messing things up.

Do you have working gauges (fuel etc- dummy lights) when the dash lights act up? How about the dome or courtesy lights?

The entire dash harness and bulbs were replaced. I'm not certain that this wasn't an issue prior either, the dash bulbs were always pretty dim. They appeared to be the originals and many of them had quite a bit of silvering on them.

One thing I've always had occur and still does (which leads me to believe this may not be an entirely new issue) is that when the lights are turned on, the fuel gauge moves towards empty.

One of the few things I did not replace recently is the printed circuit board. I'm almost wondering if there isn't an issue there. I just don't know what would be killing voltage through the dash otherwise. The ignition and the EFI is run off the battery, triggered by a relay connected to the black and pink coil wire. So there's zero load on the dash from those items. That includes the fuel pump as well.

The only thing that will still load through the dash is the headlights. I did recently install a set of aftermarket LED headlights. Thinking that could be the culprit, I completely removed the headlight socked from the plug. This made no change, so it's not the headlights that are causing the voltage drop.

the FiTech reads voltage at the battery and with or without the headlights on, the car sees a constant 13.8-14 volts from the alternator, so I can pretty decently rule that out as the cause as well.

I don't believe so. the main harness connectors can only be connected to their terminals one way. The only thing additional to the main harness is the aftermarket tach. That is receiving power from the acc terminal on the fuse box and it's light is plugged into the extra terminal found on the console harness connector.

The courtesy lights as well as the tach, console and HVAC lights function normally with key on. Basically anything on the grey wire is functioning normally.

I did not replace the turn signal harness when I replaced the dash harness.

You've got a bad or weak ground to the cluster.

Try getting a hold of the connector/plug-in and giving it a wiggle.

Lights are grounding through the fuel guage with key off. The ground path through the guages resistor is what's making the lights dim. Power on the dash light ground wire is why the fuel guage drops with key 'on'. When lights are off, the fuel guage is grounding back through the lights.

Clay

Clay, that's excellent information. I just want to make sure when you say "cluster" that you are talking specifically about the gauge pod, or are you talking more broadly about the entire dash panel which has several ground straps?

It sounds like this issue is probably more of an issue now because of the swap to the LED lights, as I've always had that issue with the fuel gauge.

My understanding is the gauge pod grounds in the bottom left (from the back) to the steel ground straps that run to the radio, up to the HVAC which and travels across the HVAC case to the final strap that grounds to the steel frame using the dash carrier's stud and affixed by a nut. Is there additional ground locations that I need to be aware of?

Yes the guage pod. The printed circuit should have at least one ground wire going ????.

Clay

EDIT

No ground wire in connector. Printed circuit must have a bare spot on the back side that bolts down some where.

This is the gauge pod as it was taken out of the car. It is attached to the dash carrier ground strap in the lower left hand corner. Am I missing a ground to the printed circuit directly?

Attachment 544704

I agree with Quick Silver, dimming dash lights and gauges reacting to dash lights on is clear indication of poor ground. LED dash lights are probably more sensitive to low voltage than filament bulbs. These year GM cars are notorious for bad dash grounds. I'd drill a 1/8 hole (carefully into the side of the cluster case (the steel part) and put in a good serrated ground wire connection direct to a ground smooth to bare steel area on the body shell itself. The factory grounds are a joke, sheet nuts tightened on plastic studs and screws into plastic housings, failure prone is a serious understatement especially when that plastic is 51 years old.

The printed circuit grounds to the cluster with that screw in the upper right area. The problem isn't that, it's the ground from the body to the cluster. Have a look at the 69 shop manual, you can see the various ground strips that ground the cluster and other dash bits (wiper switch etc) to the body shell.

Okay yeah that was my understanding. My ground straps aren't in terrible condition, but they aren't in great condition either.

Sucks that I'm going to have to take the dash out again which is a royal pain, but my plan is to put ground straps on the lower steel tabs and run them directly to the chassis.

You don’t have to pull the dash out, you can reach the bottom of the cluster just by lying underneath the dashboard.

Seeing what's going on now.... I'd be terribly tempted to just add a ground wire under that screw on top right back to something solid. And add one to that lower fuel guage stud if needed.

Been lost a minute zoomed in on your pic and trying to read a worn out schematic.

Gettin' slow-er
Clay

Yeah I think that's the plan for this weekend. It's pretty tight under there but hopefully I can get something together without having to take the dash back out.

Fiddled around with the car a bit last night and really made sure that the ground at the post by the radio and hvac was secure and tight and that really helped. I had 100% illumination from the gauges and didn't lose the gas gauge either last night.

That being said I'm still gonna crawl under this thing and add some more grounding to the cluster because it's pretty clear that lone ground isn't really sufficient and it appears to want to loosen up over time.

I really appreciate everyone's help with this!