Can a dimmer switch be bad, but still work? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

custom10nut · 07-08-2017, 09:26 PM

Can a dimmer switch still change the low beam to high beam, but be bad as far as electrical continuity goes?
My dash lights went crazy again, with the high beam indicator, and both the directional indicators stay on. Also, the only light in the dash that works is the one on the far right.
All the exterior lights work fine.
I have one of the screws on the dash housing grounded now, so I am now going to ground the other, just to make sure.

**davischevy** · 07-08-2017, 09:56 PM

The first thing I would check is the plug in the back of the cluster tight. It sounds like a ground problem. The printed circuit may be shot. These electrical gremlins can be tricky.

**davischevy** · 07-08-2017, 09:58 PM

Usually the dimmer will make the headlights go dark if it is bad.

custom10nut · 07-08-2017, 10:35 PM

Quote:

Originally Posted by davischevy

The first thing I would check is the plug in the back of the cluster tight. It sounds like a ground problem. The printed circuit may be shot. These electrical gremlins can be tricky.

The printed circuit is new. I'm going to take the dash apart tomorrow to ground the other screw, and I'll check the plug then.
I have to try to fix my tach too.

**dmjlambert** · 07-08-2017, 11:22 PM

Interesting you mention the far right light in the cluster. The ground gets to the cluster from pin 7 of the connector, and then it goes to the far right bulb and to the metal of the cluster through a screw, and then the rest of the printed circuit ground trace gets ground from the screw on the other side of the cluster. So if those 2 screws are not clean and are not making good contact with the metal trace in your new printed circuit, you could have a lack of proper ground to the cluster lights other than the far right one. Don't know if that is the whole problem, though. Here is a diagram of the cluster printed circuit.

http://67-72chevytrucks.com/vboard/s...d.php?t=709847

Husker · 07-08-2017, 11:35 PM

No Dimmer cant be bad and still change HI/LO. If it was open it would not allow current to pass.
Ron

custom10nut · 07-09-2017, 08:19 AM

Quote:

Originally Posted by dmjlambert

Interesting you mention the far right light in the cluster. The ground gets to the cluster from pin 7 of the connector, and then it goes to the far right bulb and to the metal of the cluster through a screw, and then the rest of the printed circuit ground trace gets ground from the screw on the other side of the cluster. So if those 2 screws are not clean and are not making good contact with the metal trace in your new printed circuit, you could have a lack of proper ground to the cluster lights other than the far right one. Don't know if that is the whole problem, though. Here is a diagram of the cluster printed circuit.

http://67-72chevytrucks.com/vboard/s...d.php?t=709847

This is what I'm thinking too. The problem arose after the truck sat for a while, and with the drastic temperature change from spring to summer, it probably has oxidation build up, causing the break in contact when dry. Thanks to all for the insights

leftybass209 · 07-09-2017, 12:47 PM

Electrical continuity is simply a continuous path (conductor) for electricity to flow, which can be checked using a multimeter on the ohms setting. A multistrand copper wire can check out completely fine using a continuity test, if even all but just 1 strand are broken. However, when that wire is asked to support a load, it most likely will fail due to high resistance along that single strand.

Dimmers are notorious for going bad, especially most aftermarket garbage. Check for 12v at the plug on the dimmer.

toolboxchev · 07-09-2017, 02:02 PM

You could also have a amount of corrosion at any connectors in the lighting system.

I went through my old truck and cleaned up all the grounds and the packard connections. My lights do dim ever so slightly when at idle in gear yet they are as bright as the day it came off the showroom even at 47 years with original alternator and wiring.

Its amazing what a little cleaning can do!

07-08-2017, 09:26 PM	#1
custom10nut Registered User Join Date: Apr 2015 Location: East Tn (In the heart of the Smoky Mtns) Posts: 1,846	Can a dimmer switch be bad, but still work? Can a dimmer switch still change the low beam to high beam, but be bad as far as electrical continuity goes? My dash lights went crazy again, with the high beam indicator, and both the directional indicators stay on. Also, the only light in the dash that works is the one on the far right. All the exterior lights work fine. I have one of the screws on the dash housing grounded now, so I am now going to ground the other, just to make sure.

07-08-2017, 09:56 PM	#2
davischevy Senior Member Join Date: Sep 2008 Location: Harrison, Arkansas Posts: 9,786	Re: Can a dimmer switch be bad, but still work? The first thing I would check is the plug in the back of the cluster tight. It sounds like a ground problem. The printed circuit may be shot. These electrical gremlins can be tricky. __________________ other Larry Build thread, Arkansas K10 https://67-72chevytrucks.com/vboard/...=755797&page=5 The ability to speak several languages is an asset, but the ability to keep your mouth shut in any language is priceless.

07-08-2017, 09:58 PM	#3
davischevy Senior Member Join Date: Sep 2008 Location: Harrison, Arkansas Posts: 9,786	Re: Can a dimmer switch be bad, but still work? Usually the dimmer will make the headlights go dark if it is bad. __________________ other Larry Build thread, Arkansas K10 https://67-72chevytrucks.com/vboard/...=755797&page=5 The ability to speak several languages is an asset, but the ability to keep your mouth shut in any language is priceless.

07-08-2017, 11:22 PM	#5
dmjlambert Senior Member Join Date: Apr 2016 Location: Cypress, TX Posts: 3,563	Re: Can a dimmer switch be bad, but still work? Interesting you mention the far right light in the cluster. The ground gets to the cluster from pin 7 of the connector, and then it goes to the far right bulb and to the metal of the cluster through a screw, and then the rest of the printed circuit ground trace gets ground from the screw on the other side of the cluster. So if those 2 screws are not clean and are not making good contact with the metal trace in your new printed circuit, you could have a lack of proper ground to the cluster lights other than the far right one. Don't know if that is the whole problem, though. Here is a diagram of the cluster printed circuit. http://67-72chevytrucks.com/vboard/s...d.php?t=709847

07-08-2017, 11:35 PM	#6
Husker Registered User Join Date: Dec 1999 Location: Mid NE USA Posts: 2,209	Re: Can a dimmer switch be bad, but still work? No Dimmer cant be bad and still change HI/LO. If it was open it would not allow current to pass. Ron __________________ Member #111 68 C-10 Daily Driver 70 4x4 Project 76 Jeep CJ-5 Help Support the Board: http://67-72chevytrucks.com/vboard/payments.php He who knows nothing is closer to the truth than he whose mind is filled with falsehoods and errors. Thomas Jefferson

07-09-2017, 12:47 PM	#8
leftybass209 Registered User Join Date: Feb 2011 Location: Modesto, CA Posts: 2,185	Re: Can a dimmer switch be bad, but still work? Electrical continuity is simply a continuous path (conductor) for electricity to flow, which can be checked using a multimeter on the ohms setting. A multistrand copper wire can check out completely fine using a continuity test, if even all but just 1 strand are broken. However, when that wire is asked to support a load, it most likely will fail due to high resistance along that single strand. Dimmers are notorious for going bad, especially most aftermarket garbage. Check for 12v at the plug on the dimmer.

07-09-2017, 02:02 PM	#9
toolboxchev Registered User Join Date: Jul 2015 Location: 2nd left past the stump on a dirt road. Posts: 2,629	Re: Can a dimmer switch be bad, but still work? You could also have a amount of corrosion at any connectors in the lighting system. I went through my old truck and cleaned up all the grounds and the packard connections. My lights do dim ever so slightly when at idle in gear yet they are as bright as the day it came off the showroom even at 47 years with original alternator and wiring. Its amazing what a little cleaning can do!



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