RJ1AZ

In the course of rehabbing the gauge cluster and bezel on my 69, I installed LED bulbs for the gauges. I also replaced all fuses in my fuse panel at that time. I remember testing the lights and they turned on.

Fast forward a couple months and I turn on the headlights during a drive home and the gauge lights don't come on. I've already checked the fuses.

Is it common for the headlight switch to be the source of such a problem? I'm looking for a little direction before I start tearing things apart. I know just enough about electronics to get myself in trouble, so some expert advice would be appreciated.

I'm assuming that the gauge lights utilize the short fuse located at the bottom of the fuse panel? The wiring diagram below doesn't seem to match up with that location, but maybe they didn't care about that when they drew it up.

ben dover

Do you have 12v at the hot side of the fuse? If you're sure that's the correct fuse, then the switch is not bad.

henrikse

Yes check on both sides of fuse as the contacs get corroded so go to the contact not the fuse itself. If you have it follow it on the gray wire but first ensure you have a good ground. I believe there are two tabs on the back of guages

RJ1AZ

I'm going to dumb this down, for my own benefit. With the ignition key to the first stop (accessory position), and the headlight switch ON, I set my multimeter to 20V, red lead on the left terminal of the shortest fuse, which is at the bottom edge of the fuse panel, black lead to a ground source (steering column and/or brake pedal lever). I'm getting no voltage reading.

I also checked some of the other fuses in the same manner and got a little over 11 volts.

So, I assume this means there's no voltage making it to that fuse from the headlight switch? Unless I hear other suggestions, I guess I'll pull the headlight switch tomorrow and see if there's anything obviously wrong.

henrikse

What year is your car? You do not need the ignition on to use the headlights . I believe they are hot all the time. You should always have voltage on one side of the fuse. Is your wiring diagram for your year car. Are you sure you are on the right fuse? It should say instr lamps (on my 73 it does)Do your headlights or park lights work?

carriljc

Did you "turn and/or twist" the headlight switch? I'm assuming 69 has a regular headlight switch. If so, then you turn(twist) to dim/adjust the dash lighting. Perhaps you did it inadvertently?

D_Williams

I would also suggest this. There are a few positions on my headlight switch that won't turn on my dash lights, but turning the **** a little either way will turn them on.

If that doesn't work at all, then I would suspect that your headlight switch is bad.

RJ1AZ

1969. Headlights/tail lights/parking lights are functional. Wiring diagram is for 1969. The shortest fuse does say "INST LPS", I just didn't want to assume anything.

I did try rotating the headlight switch back and forth to see if I had the lights dimmed all the way by mistake. It made no difference.

I guess my next step is to remove the headlight switch. I'll do a forum search to see if the switches are repairable, or a replacement item.

TimAT

You stated you had installed LED bulbs. I did the same on my 69. The bulbs I used require 12v and will go out with anything less. I have to run the instrument lamp dimmer at the full bright position. On the flip side, I can see the gauges very well at night.

RJ1AZ

Thanks. I'll keep that in mind.

UPDATE: I pulled my headlight switch and it was toast. The dimmer coil wire was broken. (Headlights work fine).

I installed a new switch. Then, I turned on the headlights, rotated the dimmer switch all the way on, still no instrument lights. I then checked the voltage at the fuse panel with my multimeter and wasn't getting any reading on the INST LPS fuse. I did the same check on the tail lamp circuit, just to be sure, and was getting over 11 volts.

Looking for some ideas on other things to check.

carriljc

Check the voltage at a lamp socket. Get an incandescent lamp and put it in a socket to see if it works.

Snickers1948

Just checking my 75 and it works just as you say. But if I rotate the light switch full RIGHT, I hear a relay click and voltage to Install Lts goes to about 1 volt. Full left gives 12v to the Inst lights!

henrikse

Your problem is the inst lamp fuse. When you have light switch on there should be 12 volts on both sides of the fuse. Take out fuse and visually check or use ohmmeter although I think it is good. Then take some emery cloth or fiberglass pen and clean metal tabs on each side where the fuse goes. You can spray contact cleaner but the tabs get corroded all the time and abrasive is better.
Attached wiring for my 1973 and you can find the small instrument lamp fuse on pg 1. You see one side (gray) feeds all the lights. Follow the other side of fuse and you see it goes to dk green. Follow dk green on page 2 and you will see it goes to light switch. If you have the light switch exposes still you can check at dark green on the light switch (make sure the connector is on good) If you do not have it here you got a bad light switch. If you have it it goes direct to inst lmp fuse and so on.
As well to complete circuit as mentioned before all lights go to two ground tabs that go to ground. Believe this is the ground lug above fuse box on chassis. Ensure ground is good with meter on 12 v+ battery and ground to tab if in doubt

RJ1AZ

Thanks for your reply.

I actually managed to figure this one out...at least all lights worked when I bench tested them.

I did a continuity test on my INST LPS fuse and it was good, which really puzzled me. I was getting no voltage reading on either side of that fuse in the fuse block.

I sat down with a copy of the wiring diagram and some colored markers and traced the circuits. What I found out (and is diagramed in the drawing below) is that the INST LPS fuse is not the only fuse in the circuit for the gauge lamps. The headlight switch pulls power through the TAIL fuse, then sends it down the green wire, through the INST LPS fuse, and on through the gray gauge wires to the gauge lamps.

My TAIL fuse was blown, so I replaced that. I also found a couple sketchy connections in my gauge lighting wires and I repaired those. Then I "bench tested" each individual light (dash removed) by running a ground wire to the light socket, then connecting the battery and operating the headlight switch. They all worked, so I'm in the process of buttoning the dash back up.

Peterbuilt

Five stars ***** for you for figuring it out.
I like electrical problems because once you find the problem it's an easy fix.
GM made it that way.
If only the instrument fuse blows you have no dash lights and you become alerted to a problem
If the tail light fuse blows you have no instrument lights but you won't know that the tail lights are out until you dig in, as you did.