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Old 01-26-2018, 11:41 PM   #1
jrpontiac
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Dash lights not working

Just picked up a 77 c10 and the dash lights are not working.
-The headlight switch is getting power via red wire.
- headlights, tail, idiot gauges, blinkers, high beam indicator all work.
- heater panel light and radio light do not work
- The PNL fuse is not getting power
- The green wire on the headlight switch is not getting power. I would be my understanding that the power from the green wire would come from the primary power in wire on the switch. (red wire above) I've made sure to turn the light knob to dash lights on position.
- I've replaced the headlight switch with a good switch out of my 82 c1500. Problem still exists.

Does the headlight switch have a ground, where does it terminate.

I'm guessing it is a ground somewhere but not sure where to look.
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Old 01-27-2018, 03:18 AM   #2
VetteVet
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Re: Dash lights not working

Quote:
Originally Posted by jrpontiac View Post
Just picked up a 77 c10 and the dash lights are not working.
-The headlight switch is getting power via red wire.
- headlights, tail, idiot gauges, blinkers, high beam indicator all work.
- heater panel light and radio light do not work
- The PNL fuse is not getting power
- The green wire on the headlight switch is not getting power. I would be my understanding that the power from the green wire would come from the primary power in wire on the switch. (red wire above) I've made sure to turn the light knob to dash lights on position.
- I've replaced the headlight switch with a good switch out of my 82 c1500. Problem still exists.

Does the headlight switch have a ground, where does it terminate.

I'm guessing it is a ground somewhere but not sure where to look.
The wiring patterns from GM have been pretty consistent over the years and the colors have remained for the most part the same as well. Your description follows the pattern.

One thing to mention is that the type of cluster is very important because they are wired differently at the plug. I see you have the light cluster.

You are correct that the power wire to the headlight switch is the large red wire. However this wire only powers the headlight dimmer switch.

The wire you need to check is the orange wire, which powers the tail lights and the dash lights. It is a key off powered wire, and it gets it's power from the large red wire at the fuse panel. It then sends power back to the headlight switch and connects with the brown wire, (tail and marker lights), and the green wire (dash lights). The green wire runs this power through the rheostat in the switch and back to the fuse panel to the dash lights fuse.

Troubleshooting is fairly easy.

1. Check for power on the orange wire at the headlight switch. Since you have stated that the tail lights work, then you do have power on the orange wire.

2. Pull the head light switch on, and look for power on the green wire coming from the headlight switch to the fuse panel. You state that there is no power on the green wire at the fuse panel. This indicates no connection between the orange wire and the green wire on the headlight switch. You have installed a known good switch and the problem remains.

3. Apply power to the dash lights fuse and see if the dash lights work. Use a constant hot source to avoid needing to tun the key on.

If you get dash lights, then the green wire is not transferring power from the headlight switch, through the rheostat, to the fuse panel. In other words it's open. Look for a cut wire or a poor connection on the wire, or if possible run a temporary wire from the switch to the fuse panel dash lights fuse. The green wire will be inside the harness so it may be hard to tell where the break is.

The green wire on the headlight switch would not show any power if it had any break in it because there would not be a path to ground for the volt meter to read. You would need to do a continuity check on the switch between the orange wire and the green wire and then again between the green wire on the switch and the green wire at the dash lights fuse. Remove battery power for this or you meter will object.

The heater panel light and the radio light do not work because they are part of the circuit with the dash lights. Some radio lights work from internal radio power so that may be a separate issue.

The headlight switch has to be grounded, because the white wire connected to it is the ground side wire for the courtesy lights. That has nothing to do with the dash lights not working. What happens is when the headlight knob is turned fully to the right, a connector in the switch grounds the white wire to turn on the dome and courtesy lights.

Check the picture. This is an earlier switch but I believe it serves several years.


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Old 01-27-2018, 10:49 PM   #3
jrpontiac
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Re: Dash lights not working

Thank you VV for the information. You are an asset to this forum.
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