This is weird,,,,,, wonky gauge cluster

85 CA SIERRA 1500 · Apr 6, 2020

Never seen this before,,,,,,backlight illumination for the gas-gage and speedo quite after a few minutes of switching on and then the right turn indicator stays lit up.
Thought you all would find this interesting,,,,any thoughts?
I'm thinkin maybe a bad printed circuit on the back of the cluster or the connector, or headlight switch has high resistance and overheats and shorts.

75gmck25 · Apr 7, 2020

Based on my experience, the constant turn signal light means the cluster ground wire is disconnected or broken. On your truck there should be a small ground bus/strip up under the dash, or on older trucks the black wire is connected to a screw on the emergency brake mechanism.

Bruce

85 CA SIERRA 1500 · Apr 7, 2020

75gmck25 said:
Based on my experience, the constant turn signal light means the cluster ground wire is disconnected or broken. On your truck there should be a small ground bus/strip up under the dash, or on older trucks the black wire is connected to a screw on the emergency brake mechanism.

Bruce

Thanks Bruce,,I will try to twist my old stiff body up into the dash and check for this. I did not suspect a grounding issue because the other lights work it is only the fuel and speedo that are acting up.
All the best,
Tracey>>>>>>>>>>>>>>>

Snoots · Apr 7, 2020

If the turn signal light doesn't blink, turn it on and go check the front and rear light. If it's not 'bright' replace the bulb.
The blinker will not function if there is a bad bulb.

For a grounding issue, check the left kick panel near the parking brake. There is a 'master' ground block there that usually loses it's ground.
Remove it, clean the panel and buss, coat it with copper-infused anti-seize and reinstall it.

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mtnmankev · Apr 7, 2020

On my 83 C-20 and 84 K-10 there are no separate ground wires running from the dash cluster, and both trucks have issues with the lighting.
Is the ground wire part of the multi wire connector that plugs into the printed circuit ?

tobiahr · Apr 13, 2020

Snoots said:
If the turn signal light doesn't blink, turn it on and go check the front and rear light. If it's not 'bright' replace the bulb.
The blinker will not function if there is a bad bulb.

For a grounding issue, check the left kick panel near the parking brake. There is a 'master' ground block there that usually loses it's ground.
Remove it, clean the panel and buss, coat it with copper-infused anti-seize and reinstall it.

You must be registered for see images attach

You must be registered for see images attach

I always used the dielectric grease. Is the copper anti-seize better?

Snoots · Apr 13, 2020

tobiahr said:
I always used the dielectric grease. Is the copper anti-seize better?

Di-electric grease is non-conductive. It's GREAT for preventing bulb contacts from corrosion by displacing moisture.
Copper anti-seize will prevent corrosion AND give you the conductivity you need for a good ground.

HINT: You only need to get a little on the connector; use a Q-Tip. Just be sure to coat any bare metal.
Do this for EVERY ground on your truck.

A small tube of anti-seize costs a lot less than headaches.

Snoots · Apr 13, 2020

mtnmankev said:
On my 83 C-20 and 84 K-10 there are no separate ground wires running from the dash cluster, and both trucks have issues with the lighting.
Is the ground wire part of the multi wire connector that plugs into the printed circuit ?

Don't quote me but I believe there is.

85 CA SIERRA 1500 · Apr 13, 2020

Well gang,,,,this is the latest in my quest to fix the wonky dash cluster.
As all of you have advised, I finally found the elusive central grounding point. It was up under the dash, behind the cluster bolted to the wall above the parking brake. Wish it had been behind the kick panel like everyone else's. Would have been way easier to work on.
I removed the "tab-plate"(not sure what the proper name is), scuffed it up with a wire brush and a knife all nice and shiny, wire brushed the wall down to bare metal, wire brushed and cleaned the bolt, wire brushed the ring terminal that goes under the bolt, slid the slide terminals on and off the tabs several times.
Managed to break some of the 35year old plastic on the cluster.
Put everything back together,plugging the speedo cable back on was, shall I say a challenge. Hopefully it is properly engaged.
After all this I wish I could say that the problem is fixed, but then I would be lying.
Do you guys have any other ideas, as it is now the gas gage only works if the dash lights are off, if I turn the headlite switch knob to the left and send power to the gage lites the right turn indicator lights up steady and the gas gage dives to empty, and the lights for the speedo and gas gage stay out.
All the best,
Tracey>>>>>>>>>>>>>>>>>>>>>

Turbo4whl · Apr 13, 2020

85 CA SIERRA 1500 said:
Well gang,,,,this is the latest in my quest to fix the wonky dash cluster.
As all of you have advised, I finally found the elusive central grounding point. It was up under the dash, behind the cluster bolted to the wall above the parking brake. Wish it had been behind the kick panel like everyone else's. Would have been way easier to work on.
I removed the "tab-plate"(not sure what the proper name is), scuffed it up with a wire brush and a knife all nice and shiny, wire brushed the wall down to bare metal, wire brushed and cleaned the bolt, wire brushed the ring terminal that goes under the bolt, slid the slide terminals on and off the tabs several times.
Managed to break some of the 35year old plastic on the cluster.
Put everything back together,plugging the speedo cable back on was, shall I say a challenge. Hopefully it is properly engaged.
After all this I wish I could say that the problem is fixed, but then I would be lying.
Do you guys have any other ideas, as it is now the gas gage only works if the dash lights are off, if I turn the headlite switch knob to the left and send power to the gage lites the right turn indicator lights up steady and the gas gage dives to empty, and the lights for the speedo and gas gage stay out.
All the best,
Tracey>>>>>>>>>>>>>>>>>>>>>

So probably still a ground issue. The ground on the printed circuit may have a break in it.

Turbo4whl · Apr 13, 2020

Also check the plug going to the printed circuit, maybe the pin pushed out. You need to pull the cluster again but this time you have some practice with the speed-o cable.

75gmck25 · Apr 14, 2020

A missing ground causes unpredictable problems because circuits will often "find" a missing ground path when something else is turned on or off. I have never figured out the turn signal indicator path and why it turns on solid, but its a very common sign of a missing ground on the cluster.

One suggestion for the speedometer cable is to make sure you have the right cable. The first one I purchased had a threaded fitting on the speedometer end, and I could just barely snap it into the spring clip on the back of the speedometer. It worked for a while, but then popped out consistently. I went back to Auto Zone and finally found the right cable, which just has a flared metal fitting on the end. That flared area snaps very positiively under the spring clip on the back of the speedometer.

IIRC, you push the springy part back toward the edge of the speedometer and that opens it up into the larger diameter part of the spring clip. Then push the cable in firmly so it engages with the speedometer, and let the clip spring back so it holds against the flared area.

If you look at this set of cables, the correct one had ends like the CA-3003 cable, but the one they sold me first had ends like the CA-3016 cable. https://www.autozone.com/drivetrain...cable&fromString=search&isIgnoreVehicle=false

Bruce

Big Chip · Apr 14, 2020

I find it easier to reach up under the installed cluster to unhook and hook up the speedo cable.

85 CA SIERRA 1500 · Apr 14, 2020

Thank you all for the quick and helpful responses.
I did pull the plug from the gage cluster and checked that all the contacts both on the plug and the circuit board looked clean and shiny but did not know to check the wires, did not know that they can work loose from the actual plastic plug. I guess that is kinda dumb on my part, just was not thinking clearly.
Thanks for the tip on unconnecting the speedo cable before pulling the cluster.
If it turns out that the circuit board is bad and I have to get a new one from LMC it might be a good excuse to up-grade with the Tach conversion,,,funds permitting,LOL.
Thank you again to all that have jumped into this thread. You have all been a great help and have helped me deal with my own frustration.
All the best,
Tracey>>>>>>>>>>>>>>>>>>.

Spunbearing · Oct 9, 2022

I had a similar issue with a 72 Chevy back in the early 90's. I ended up soldering a new ground wire to the circuit board on the ground track and secured the other side to the sheet metal with an eye and self tapping screw. I came across this thread because I'm having an issue with my 84 square body, and I was hoping I wouldn't have to go through all of that again..... but so it goes.

This is weird,,,,,, wonky gauge cluster

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