Dash Lights-Dimmer??? (68 B)

Posted By: plysat

Dash Lights-Dimmer??? (68 B) - 03/02/12 11:45 PM

Here's a fun one... The other night my dash lights were out, so I thought I'd fiddle with the thumb wheel dimmer and... no effect on the dash lights but at a certain point both TS indicators and the oil idiot light indicator came on... ??? The dome light still comes on and off as it should. Any ideas? Bad thumbwheel dimmer? It's a weird one. Thanks!

Posted By: 68HemiB

Re: Dash Lights-Dimmer??? (68 B) - 03/03/12 12:13 AM

Quote:

Here's a fun one... The other night my dash lights were out, so I thought I'd fiddle with the thumb wheel dimmer and... no effect on the dash lights but at a certain point both TS indicators and the oil idiot light indicator came on... ??? The dome light still comes on and off as it should. Any ideas? Bad thumbwheel dimmer? It's a weird one. Thanks!

Symptoms like this often have as their cause an open ground side of the circuit.

What happens is that the current is finding an alternate path to ground, through the filament(s) you describe. If the engine was running [and had oil pressure] at the time, that portion of the symptoms is not so obvious. The turn signal indicators fit with the textbook "common ground open, feeding back through filament(s) to an alternate ground" scenario.

If you check the printed circuit on the back of the cluster, you should be able to trace the common ground, and clean or reconnect or provide an alternate connection to a solid ground somewhere on the dash frame or firewall.

This is not to say that dimmers in 45 year-old cars aren't prone to open/dirty rheostats. It's just that your symptoms point to a grounding issue.

Posted By: plysat

Re: Dash Lights-Dimmer??? (68 B) - 03/03/12 01:08 AM

That'll be fun

... this may be a silly question, but the last time I was in the car I hit the high beam switch, which I probably haven't done in years. I've heard those can cause weird problems too. Possibility? I do have a new PC board, and I probably should get a new thumbwheel dimmer as mine has been sort of funky for the 20 years I've owned car, but never anything like this...

Posted By: 68HemiB

Re: Dash Lights-Dimmer??? (68 B) - 03/03/12 04:46 AM

The fault is probably NOT on the printed circuit itself (end even less likely in light of its recent replacement), but in WHERE THE GROUND TRACE of that printed circuit connects to the dash frame, especially in light of the recent meddling in that very area.

The high beam switch has nothing to do with this.

It's not voodoo.

really.

Posted By: Jim_Lusk

Re: Dash Lights-Dimmer??? (68 B) - 03/03/12 05:16 AM

Quote:

It's not voodoo.

really.

You are quite correct. It's magic (but a special kind that I can't say on here......).

Posted By: plysat

Re: Dash Lights-Dimmer??? (68 B) - 03/03/12 05:34 AM

Heh... thanks, I actually haven't replaced the PC board yet... Was trying to avoid diving into that... I'll trace the ground first... I'm actually not too bad with electrical witchcraft, it's the laying upside down in a pretzel shape trying to trace wires that I'm getting tired of.

Quote:

The fault is probably NOT on the printed circuit itself (end even less likely in light of its recent replacement), but in WHERE THE GROUND TRACE of that printed circuit connects to the dash frame, especially in light of the recent meddling in that very area.

The high beam switch has nothing to do with this.

It's not voodoo.

really.

Posted By: Jim_Lusk

Re: Dash Lights-Dimmer??? (68 B) - 03/03/12 06:06 AM

If there's that much work to do on your backside, remove the front seat. Believe me, the time spent pulling the seat will be worth it.