Instrument panel light dimmer

[John85SS]

My IP lights were always dim and the dimmer has never worked. You can rotate the headlight switch all the way in either direction and it does not change the brightness. I thought it was the headlight switch so I bought a new one. Made no difference. I pulled the IP panel out I bought led bulbs and while it was out I probed pin 5 with the park lights on and I had 11.5 volts there no matter what I did with the headlight switch rotation. Any ideas what could be causing this. Bad new switch?

 

[ELCAM]

Power into the headlamp switch is the 12Ga red wire, the dimmer rheostat is fed off the switch contacts inside the switch for the park lights.

There should be a dark green wire coming from the headlight switch going to the fuse box to the inst lps fuse, goes out that fuse to a gray wire to the gauge cluster for the dash illumination.

I would pull the fuse, remove the headlight switch still connected, turn the headlight switch on and see if the dark green wire varies with the dimmer rheostat. If it does put the fuse in and see if the gray wire does the same thing (you can test at the fuse so you don't have to pull the gauge cluster again, with the fuse out and the lights on see which one has voltage that will be the green one plug the fuse in and test the other one.). If not It might be getting fed somehow by another circuit in the fuse box.

 

[John85SS]

Thank you! I will try this tomorrow and report back. What you said makes sense. I am the 3rd owner of this car and back in the 80’s it was stolen and stripped. The second owner pieced it back together so hard to say if everything got hooked back up properly. Nice to have a direction to go with testing now.

 

[John85SS]

At the green wire directly from the new headlamp switch with park lights on I get no voltage change. Stays the same no matter rheostat position. Has to be the switch then right? The new one I bought was brand Standard. I can buy a GM one from RA so thinking about ordering that.

 

[ELCAM]

You did pull the fuse before you tested it? If it is being back fed testing might not give accurate results.

Otherwise unless the wires are in the connector incorrect it would appear the switch is bad.

With the switch out and in your hand like it is installed, wiring up. There are three terminals across the front running side to side the green is the middle one.

 

[maxi426]

Does this car have an aftermarket radio installed, or any kind butchery in the radio harness? If it does, disconnect every wire from it, and retest. Some aftermarket radios have a connection to the dash illumination circuit. Could be be back feeding, or connected incorrectly. Inspect for any kind of previous wiring mods.

 

[ELCAM]

Maxie426 I think you are on to something there. Been trying to think of a simple straight forward way this circuit could have this issue and I think you figured it out.

 

[John85SS]

I forgot to pull the fuse. It does have an aftermarket radio. It is just a cheap Bluetooth Dual media. I ordered a genuine GM replacement switch today from RA. Seems crazy that a new switch would have the same issue my original switch did. I tend to agree with you both something is backfeeding full batt power to the IP lights. It has been freezing cold here since Sunday afternoon. As soon as it warms up here I will retest with the fuse out, then pull the radio. If I remember correctly the wire for the factory radio light is still back there and taped off. Great info guys thank you.

 

[John85SS]

Got the new AC Delco switch today. Surprise it has the same issue as my original and the Standard brand switch I bought recently. No change in volts at the green wire out of switch with park lights on and rotating switch rheostat. This is confirmed with the 5 amp panel lights fuse pulled. Has to be getting backfed from somewhere like you both said.

 

[John85SS]

I am going to pull the radio this weekend to check on that. Also my ashtray if there was one under the radio (my ashtray is missing) would it have had a light? I think there was a connector with a bulb socket just shoved behind the radio. Wonder if that could be a suspect as well.