Instrument Cluster Lights and Dome Light

[grwindmill97]

First: I know that this topic has been discussed ad nauseam. I have read tons of threads with great troubleshooting advice, but I can’t seem to find a good solution to my problem.

Second: Full disclosure, I know next to nothing about electrical troubleshooting, please be kind.

I have a 1984 K10 and I am having issues with dash illumination and the interior dome light. There is no power to the dash lights and the dome light will not come on.

I tested the dome with a light tester and there is power coming to the bottom prong. When I put a light bulb in, the wiring gets extremely hot to the point of smelling, and the bulb never illuminates. I traced the wiring and can find no visible signs of wear. Occasionally when troubleshooting this, the horn fuse will blow. The courtesy switch springs on the door seem to be fine and are not stuck. The cigarette lighter is also working.

I pulled out the instrument cluster in the dash and started my troubleshooting there. First things first, I replaced the headlight switch. The PO replaced the stock gauges for the mechanical variety. In doing this he spliced into the brown wire coming from the light switch plug. There was a separate ground added for this and once I connected it, those lights started working. The lights that illuminate the gas gauge and speedo are not coming on. I don’t like splicing into wires, so I removed the splice into the brown wire and will replace with the correct gauges to fit the instrument panel. I pulled up the headlight switch plug diagram and found that the green wire for the dash lights was missing. I found it tucked behind some other wiring with the connection taped off. I plugged the green wire in and still no dash lights. I turned the dimmer all the way counter clockwise to where the dome light should come on and blew the taillight fuse. This fuse only blows when the green wire is plugged in.

The 5amp INSTLPS fuse has no power going to it. The green wire plugged into the headlight switch does have power. All of the wires on the switch have power except the white. The gray wire going to the printed circuit has power. I thought maybe it was the circuit, so I took the instrument panel from an 86 K10 I have and swapped it in, it made no difference.

Tonight I was doing some more troubleshooting and anytime I plug the green wire into the headlight switch, the white rheostat casing gets VERY hot and starts to smell. I expected to pull the green wire out and it to be hot to the touch, instead I noticed that the yellow wire was getting very hot.

After this I decided to come inside and ask for advise before I catch the damn thing on fire troubleshooting.

Something makes me think that the issue with the dome lights and the dash lights are related, but I’m not quite sure how to figure that out.

Any help is greatly appreciated, I said it before and I’m sure it is very evident from my questions, but I have no idea what I’m doing.

 

[mtbadbob]

Sounds like something is shorted, have you replaced the headlight switch? That basically controls everything you're having issues with. I'd start there!

 

[Dave M]

With the dome light, check that you have the correct bulb, we have seen this before a few times.

 

[AuroraGirl]

With the dome light, check that you have the correct bulb, we have seen this before a few times.

and maybe the contacts if rusty at all. Good tip. For dash illumination, could a incorrect bulb shoved into dome make all the lighting not work or would that be its own

 

[grwindmill97]

With the dome light, check that you have the correct bulb, we have seen this before a few times.

Thanks, I feel pretty stupid since I now remember reading another post saying that also…put the correct bulb in and that’s working. Still no dash lights, but I haven’t had time to continue troubleshooting that one.

 

[AuroraGirl]

Thanks, I feel pretty stupid since I now remember reading another post saying that also…put the correct bulb in and that’s working. Still no dash lights, but I haven’t had time to continue troubleshooting that one.

almost makes me to say try a new light switch then since one function is working and they are known to be eh once worn and old. newer switches which dont carry the current of the output like these tend to last longer and probably material quality or design improvements over time too.

 

[grwindmill97]

almost makes me to say try a new light switch then since one function is working and they are known to be eh once worn and old. newer switches which dont carry the current of the output like these tend to last longer and probably material quality or design improvements over time too.

I replaced the light switch before I started the other troubleshooting. I’m pretty sure it’s working because when I rotate the dial, the rheostat is cutting the voltage to the green wires connection at the most dim position. The yellow wire that comes out of the light switch is no longer has voltage at any position. As I understand it, that wire runs to the dimmer switch.

I guess my next step is going to be taking the fuse block off of the firewall and verifying proper connection.

 

[AuroraGirl]

Wait, I want to be clear here. Dimmer switch is your dash illumination only, not your... column? mounted high beam switch? Is your column the right one? The floor switch, for example in my truck, would be unsurprsing to have a wiring problem because of how shot my floor is. that physically wires to a bulb socket on the printed circuit and if you meant that that one was not working, maybe printed is allowing that to ground the lamps or whatever , but then I think you mean the other stuff. does high beam work anyway i guess too

I had a mix up with someone on buick forums because He most definitely meant the column mounted flash to pass high beam detent switch thing in the column than his simple stalk, when i thought he meant dash illumination.

thats something I would say, examine your sources using the light on that circuit. the radio, washer switch, the hvac panel. those bulbs all ok?Column wasnt changed or rewired and ignition switch is working right(just general idea checks)

 

[Grit dog]

…

 

[Raider L]

@grwindmill97,

You and I would be the blind leading the blind when it comes to electricity so don't feel alone. Ha, ha.
Go to this forum's "library" and find the schematic for your truck so that when you are staring at the fuse block wires you'll have something else to look at to make sure wires coming in from the engine bay are the correct wires going into the cab. Don't be surprised if they are not the way the schematic shows they should be, it's okay. Just look at where the wires go to each component like the dome light and where it's coming from on it's way to the dome light. Whoever monkeyed with the wires probably messed up more than you've found already. Whoever switched out the gauges mixed up wires to. I agree that you have a dead short somewhere. You're going to have to find it. Obviously, when you find it all will be well. There may very well be a short in the engine compartment possibly, something is "on" all the time feeding the panel lights and the interior lights at the same time. Could be interior lights have been connected together with the dash lights.
Let me ask you this. When you are doing this testing on the dash/interior lights, do you have the doors open or closed? That might make some difference. Then you can change a wire, then open the doors and see what happens. Close the doors, change a wire, then open the doors again until something works right. Kinda of a process of elimination. What about the courtesy light near the heater vent down there? That light can come on when you open the doors and when the doors are closed.
Just some stuff to think about.
When I worked on passenger aircraft the schematic's were huge. Many times I would just follow one of the senior mechanics around looking at wires here and looking at wires there, back and forth to the schematics until he got it narrowed down. Sometimes it was interesting.

 

[Ellie Niner]

I replaced the light switch before I started the other troubleshooting. I’m pretty sure it’s working because when I rotate the dial, the rheostat is cutting the voltage to the green wires connection at the most dim position. The yellow wire that comes out of the light switch is no longer has voltage at any position. As I understand it, that wire runs to the dimmer switch.

I guess my next step is going to be taking the fuse block off of the firewall and verifying proper connection.

Yes. The yellow wire should be the feed to your headlights... powered only when headlight switch is pulled out to second stop. With no power coming into the dimmer switch from it, you won't have headlights.

If there's voltage being dropped on one side of the rheostat, there are lights somewhere that are working- whether this be radio, heater control, 4wd selector. If there's no load on the rheostat, it will just measure 12v no matter what the position of the wiper contact around the resistor (that spring shaped thing that wraps around the light switch). Your voltage at the panel light fuse on the fuse block will vary, too.

 

[grwindmill97]

Okay, I finally had time to finish troubleshooting this issue and here is what I found:

Pulled the cluster out again and was planning on giving up and just jumping the gray wire that powers the lights from cluster harness. I traced that wire to two larger gray wires that tied into the dash lights but also two other wires, one for the heater light and the other for the radio. I put power to the gray lead for the dash lights and they came on and worked according to the varied power from the rheostat. I put power to the lead for the radio and the tail lamp fuse blew. I put power to the lead for the heater lamp and the light came on. Now that I knew my problem was related to the radio illumination I started tracing wires and found that the PO had taped together the illumination wire and the ground wire, rolled it up and tucked it out of sight. I removed the ground from the wire, taped it up for now, and re-tested. Everything worked as it should. I wired the 3 gray wires back up the way the should be and re-tested. Still working as it should.

I’m a little embarrassed at how long it took me to figure this out, I hadn’t even considered a short at the radio. Oh well, onto the next issue, and there are plenty!