For you electrical guru's

Reply Subscribe

Thread Tools

Search this Thread

Mar 26, 2006 | 05:12 PM

78pacer

Thread Starter

Drifting

Joined: Aug 2004

Posts: 1,327

Likes: 5

From: 2010 C6 Grand Sport Convertible

For you electrical guru's

My 1978 pace car has recently developed an electrical gremlin. My temp gauge works fine until I pull my headlight **** out one or two clicks. As soon as power is applied to the circuit, the temp gauge vascillates and rapidly pegs all the way to the right stop. When I push the **** back in, the gauge returns to a normal reading. This has just developed since bringing her out of storage. I suspect the cluster is recieving voltage incorrectly to the temp gauge. This problem happens whether the engine is running, or not. (turning the key to the ON position). I can remove the gauge cluster, but wouldn't have a clue what to look for go from there. Any help is greatly appreciated.
Mike

Mar 26, 2006 | 05:25 PM

big_G

Le Mans Master

Joined: Jul 2005

Posts: 5,752

Likes: 4

From: Austin Texas

One of the paths on the gauge circuit board contains the ground for the gauges. Make sure the contacts are clean. I gently clean the finger contacts with a pencil eraser.

Mar 26, 2006 | 05:34 PM

icanfixitforyou

Burning Brakes

Joined: Jan 2006

Posts: 876

Likes: 1

From: Same as our leaders Out of my mind

Quote:

Originally Posted by big_G

One of the paths on the gauge circuit board contains the ground for the gauges. Make sure the contacts are clean. I gently clean the finger contacts with a pencil eraser.

Bad ground circuits usually cause these kinds of problems.

Mar 26, 2006 | 06:39 PM

78pacer

Thread Starter

Drifting

Joined: Aug 2004

Posts: 1,327

Likes: 5

From: 2010 C6 Grand Sport Convertible

You folks are fantastic. But being somewhat thickheaded, and realizing now I should have paid closer attention during auto shop in the '70's....I guess my question is, how does current arch from the instrument backlight circuit strip to the temp gauge strip? I could imagine the gauge pegging all the time when the key is on, headlight switch on or off, indicating a poor ground, but to have that happen soley by energizing the headlight circuit boggles me.

Mar 26, 2006 | 06:53 PM

Bruce C

Instructor

Joined: Mar 2006

Posts: 124

Likes: 1

From: Bowmanville Ontario

When you pull the headlight switch, your dash lights should be coming on at same time. Some of those lights share same ground connection, so you would be increasing load through bad connection.

Mar 26, 2006 | 06:56 PM

mrvette

Team Owner

Joined: Jul 1999

Posts: 65,492

Likes: 230

From: Orange Park Florida

Quote:

Originally Posted by 78pacer

OK, without getting too specific on account of I don't know specifically about '78 vette wiring, as opposed to my '72 here, what happens is the 'headlight' are not in the circuit you talking about even though the same switch also pulled out to the first stop activates the dash lights...and running lights....so when the dash lights are activated, they draw much more current (power) due to much lower internal resistance of the bulbs...so if you have a bad ground anywhere from the instrument panel to the birdcage then from birdcage to FRAME, you have what's known electrically as a 'floating neutral' or ground in auto terms....so the gauge in question is fine as long as the bulbs on that same display are not energised, when they are, the ground/frame/bird cage referance of the gauges is all of a sudden interrupted and the gauges go crazy....you got 12 volts or something close enough to interrupt the proper gauge operation..on the GROUND leg of your display/housing/wiring/ of the gauges....

hope this is clear enuff, as I had a couple beers by now...long day...

GENE