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Old 04-20-2017, 05:32 AM   #1
kansasc10
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Gauge cluster bulbs stopped working except for one.

I have a 72 C10 with a stock gauge cluster that I am having issues with. A few nights ago, I got into the truck and suddenly all of the gauge lights stopped working. The blinkers still lit up and the interior dome light still worked but no lights on the fuel, speedo, temp, oil or any of the gauges. So last night, I moved the ground to a different location and now 1 of the bulbs is lit but none of the others.

Some possible pertinent background....
All the wiring and fuse box was replaced last year with a painless 28 circuit wiring harness and every single electronic device on the truck has worked flawless until this issue.
- I dont have any aftermarket electronics. All stock.
- I took out all of the bulb holders and bulbs from the back of the gauge cluster, and one at a time inserted them into the 1 and only hole that will light up and verified that all the bulbs and bulb holders are working. I replaced all the bulbs back in their original locations but still only getting the one hole to light up.
- I replaced the headlight switch but that didnt fix it.
- The trace board on the back of the gauge cluster that the bulbs screw into is new.
- The blinkers still light up on the cluster, and on the front and back of the truck
- Headlights work fine both high and low beam.
- Tail lights and brake lights work fine.
-Gauges are all working fine.
- The little red light on the clusternthat tells me when I have my high beams on, is still lighting up red.
- The dome light still works fine.
- The one bulb that is working will dim like its supposed to when twisting the headlight switch.
- I deleted the connector that was on the ground wire and tried wrapping the bare wire around one of the screws that holds the metal plate directly under the steering column to make sure I didnt have a bad ground connector. Still just the 1 bulb lit up.
- I have 3 additional grounds, one from the motor to the frame, one from the cab to the frame and one from the motor to the cab. All 3 ground straps were bought new about 6 months ago and I checked to make sure they were all clean and tight.
I pulled the whole cluster panel out to inspect it and it looks fine. The connector that goes to the guages looks great.

What am I overlooking? If somehow I have a ground issue, would I still have 1 bulb working? Ive checked everything I know to check and went so far as to unhook EVERYTHING under the dash and made sure all connectors were still good and no shorts or frays. Everything still looks basically brand new and I didnt see anything suspect. So Im back to square one....everything on the truck works

Im at a loss on what to do next. If anyone has any ideas on what I can try I would sure appreciate the feedback.

By the way...the bulb that is working is the one on the very far right, closest to the passenger side. The one that lights up the fuel guage and some of the oil pressure gauge.
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Last edited by kansasc10; 04-20-2017 at 05:43 AM.
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Old 04-20-2017, 11:36 AM   #2
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Re: Gauge cluster bulbs stopped working except for one.

I have the exact same issue. I think it's a grounding problem. I just replaced my circuit board, and at first everything worked great, but the other night it went haywire. My dimmer switch want working either but now it is
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Old 04-20-2017, 11:46 AM   #3
ray_mcavoy
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Re: Gauge cluster bulbs stopped working except for one.

Quote:
Originally Posted by kansasc10 View Post
What am I overlooking? If somehow I have a ground issue, would I still have 1 bulb working? Ive checked everything I know to check and went so far as to unhook EVERYTHING under the dash and made sure all connectors were still good and no shorts or frays. Everything still looks basically brand new and I didnt see anything suspect. So Im back to square one....everything on the truck works

By the way...the bulb that is working is the one on the very far right, closest to the passenger side. The one that lights up the fuel guage and some of the oil pressure gauge.
Yes, I believe you are dealing with a ground issue.

If you look closely at the printed circuit, you will find that there are 2 traces with grounding screws going through them. One screw (right next to the plug) only serves to ground that one light on the far right that is working. The other screw grounds the remaining lights that are not working ... check that screw to make sure it is tight and making good contact with the printed circuit trace.

EDIT: I added a pic with arrows pointing to the two ground screw locations.
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Old 04-20-2017, 11:58 AM   #4
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Re: Gauge cluster bulbs stopped working except for one.

Thanks Ray
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Old 04-20-2017, 02:49 PM   #5
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Re: Gauge cluster bulbs stopped working except for one.

Your gauge lights are powered by the gray wire which goes to terminal 8 on the cluster plug on the original harness, and they are grounded to the cluster by two small screws which fasten the copper strip to the cluster metal. Your harness wires are not colored the same as the factory wires which will make it more difficult to follow the wiring.

This diagram shows the circuit and it should help you figure out where the problem is.
The picture does not show the copper strips but it has colors in place to help trace the path of the circuits.

Notice the number 8 terminal on the cluster plug with the gray colored line going to the right hand light and to the other lights on the cluster. I think you might have a tiny fracture in this copper strip which would account for the symptoms you have.

Ray beat me to it.



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The orange line is the ground line for all the bulbs, and you say that all but the three instrument lights are working. Plus you have checked the grounds to the cluster and added some.

You can trouble shoot the cluster if you remove it and apply 12 volts to the no.8 terminal and ground the two small screws. The lights should come on.
If the same three fail to light then apply power to the first light past the fuel gauge . Then the next in line. Be careful not to short the power to the ground strips (orange).

Or you can do a continuity check on the power line for the lights from terminal 8 to the last power point on the light farthest from the number 8 terminal to see if there is a break in the strip.
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Old 04-20-2017, 05:06 PM   #6
kansasc10
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Re: Gauge cluster bulbs stopped working except for one.

You guys are the best. I'll check the screws and make sure they are making contact when I get home. I'll report back what happens. Fingers crossed!
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Old 04-20-2017, 05:12 PM   #7
kansasc10
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Re: Gauge cluster bulbs stopped working except for one.

I just noticed something. It looks like the orange ground line that grounds the three bulbs also grounds the left and right turn signals. My left and right turn signals are working fine. If there was something amiss with the orange line would my blinkers still light up?
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Old 04-20-2017, 09:46 PM   #8
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Re: Gauge cluster bulbs stopped working except for one.

Quote:
Originally Posted by kansasc10 View Post
I just noticed something. It looks like the orange ground line that grounds the three bulbs also grounds the left and right turn signals. My left and right turn signals are working fine. If there was something amiss with the orange line would my blinkers still light up?
That is correct and that is why I suspect the gray power wires, as they are the only connections to the three lights that don't work.
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Old 04-20-2017, 10:50 PM   #9
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Re: Gauge cluster bulbs stopped working except for one.

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Old 04-21-2017, 11:45 PM   #10
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Re: Gauge cluster bulbs stopped working except for one.

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Old 04-22-2017, 06:52 AM   #11
kansasc10
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Re: Gauge cluster bulbs stopped working except for one.

Found the problem! At least Im 99.9% sure I did. In the pic you can see where one of the traces is broken and no longer connected, stopping the flow of power from getting to the other bulbs.

Now I need to find something thats conductive to jump to gap. Any suggestions on how to get it connected again?
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Old 04-22-2017, 10:12 AM   #12
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Re: Gauge cluster bulbs stopped working except for one.

for the length of time and effort it would take to repair it, I would simply replace it.
I have a boatload of those (non-tach) printed circuits hanging in the basement....and I think a few other guys do to.
They are easy to test to ensure continuity and thus ensure you are replacing the bad one with a good one.
That one looks like a replacement (non OEM)...correct me if I'm wrong.

All good
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Old 04-22-2017, 10:32 AM   #13
kansasc10
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Re: Gauge cluster bulbs stopped working except for one.

Its a replacement from LMC. I just bought it not too long ago which is why I was wanting to at least attempt a repair. I figured if Im gonna buy a new one anyway it doesnt hurt to at least try something. Was contemplating removing the insulation from a strand of wire and using the strands to make the connection. WOuld a bead of super glue completely ruin the circuits? Like I said, if I completely destroy it, thats ok being that Im probably looking at buying a new one anyway.
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Old 04-22-2017, 02:35 PM   #14
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Re: Gauge cluster bulbs stopped working except for one.

I did exactly what you said above, I removed the insulation from a small piece of wire, hammered it flat, and glued it in place. Mine was where the ends make contact with the plug tho. Use dielectric glue, get from any lowes, home depot, wall world, etc.. Mine has been working for almost a year now, but ii'm just to cheap to buy one, lol, good luck, I'll be watching
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Old 04-22-2017, 03:03 PM   #15
berch 69GMC
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Re: Gauge cluster bulbs stopped working except for one.

Auto bookmark any Vettevet descriptions if you like knowledge. Great asset to the site, thanks.
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Old 04-22-2017, 03:35 PM   #16
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Re: Gauge cluster bulbs stopped working except for one.

Same troubles....sweet truck btw
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Old 04-22-2017, 07:08 PM   #17
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Re: Gauge cluster bulbs stopped working except for one.

Back in my early career I used to fix broken computer circuit boards by soldering a piece of wire across cracked etches. I would scrape off the masking on each side of the break which would allow the solder to flow, and then solder a short piece of wire to bridge the gap.

Has anyone tried this on a dash circuit board?
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Old 04-22-2017, 07:30 PM   #18
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Re: Gauge cluster bulbs stopped working except for one.

Quote:
Originally Posted by ohboy321 View Post
Back in my early career I used to fix broken computer circuit boards by soldering a piece of wire across cracked etches. I would scrape off the masking on each side of the break which would allow the solder to flow, and then solder a short piece of wire to bridge the gap.

Has anyone tried this on a dash circuit board?
Yes, I have repaired quite a few instrument cluster flexible printed circuits by soldering in small pieces of wire to replace damaged traces. It's not quite as easy as working with a rigid PC board though. Mostly because the plastic backing has a tendency to melt if you hold the soldering iron on it too long. But as long as the soldering is done quickly, it usually works out pretty good.

Here is one I repaired on a mid 90's Oldsmobile instrument cluster:

After soldering the wires, I put a little bit of epoxy over the repair to help keep the wires in place.
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Old 04-23-2017, 06:11 AM   #19
kansasc10
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Re: Gauge cluster bulbs stopped working except for one.

I was thinking about dropping a spot of solder on the broken connection but thought it would just burn through. Looks like if done correctly you can get it to work. Good to know that there are a couple of options for repairing if the issue ever comes up again.


Being that I live so close to LMC, I figured Id better do it right and went in and bought another printed circuit today. Happy to report that all lights are back on and working again! Not only did I get my issue resolved, but I learned some things in the process. Excellent work to all and much appreciation for sharing your knowledge. Teach a man to fish....

Add another to the list of guys with printed circuits hanging in the basement.

Last edited by kansasc10; 04-23-2017 at 06:12 AM. Reason: Corrected typing error
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