18243
guage problem ?
Thread Starter
Racer
Joined: Feb 2001
Posts: 315
Likes: 0
From: Pensacola Florida
guage problem ?
I have a 1977 Corvette with automatic transmission. I replaced the lower dash pad (next to the drivers side door) and the center guage bezel. All guages were working properly before change. I reconnected all the guages and everything was working properly, or so I thought!
Guages all work until I put the lights on. As soon as I put the parking lights on or headlights on, the needles on every guage except water guage, stop working. All the needles go to the left. Once I turn the lights off, guages start working again!!!
Any idea what the problem could be?
It took me quite awhile to put everything back together, but I don't know where to start.
Thanks
Larry
Guages all work until I put the lights on. As soon as I put the parking lights on or headlights on, the needles on every guage except water guage, stop working. All the needles go to the left. Once I turn the lights off, guages start working again!!!
Any idea what the problem could be?
It took me quite awhile to put everything back together, but I don't know where to start.
Thanks
Larry
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,847
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Your problem is the headlamp switch grounding circuit. When you have a problem with this and pull the lamps on, the circuit will back feed voltage to the small gauges and knock them out.
When you had the pad out, did you install the switch grounding bracket? This is a thin metal strip that is mounted between the headlamp switch and the back side of the dash pad. It runs from the switch to the speedometer metal can for grounding. If this is off the car it could and probably is your problem. I'll see if I have a picture for you.
If you did place this in the car, then you'll need to go to the grounds on the speedo/tach housing, and/or the center gauge grounds.
Willcox Inc.
When you had the pad out, did you install the switch grounding bracket? This is a thin metal strip that is mounted between the headlamp switch and the back side of the dash pad. It runs from the switch to the speedometer metal can for grounding. If this is off the car it could and probably is your problem. I'll see if I have a picture for you.
If you did place this in the car, then you'll need to go to the grounds on the speedo/tach housing, and/or the center gauge grounds.
Willcox Inc.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
It is a grounding problem as Wilcox describes. The switch is looking for its ground path to the chassis [frame and back to negative side of battery]. The bracket could be missing or not making good contact; or the ground problem could be at the speedo head and it may not be grounded properly. Using an ohmmeter to test for ground may be misleading, as the ground can be present but inadequate to carry the current needed to power the lights. Good luck on your search. 
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
I agree its a ground problem but just for fun I'm going to disagree as to what the ground problem is.
I don't buy the headlight grounding bracket as the cause because that bracket only does 1 thing, it provides a ground for the white wire side of the courtesy lights so turning the **** can turn on the courtesy lights.
IMO you guys are faulting the headlight switch when the problem is the lack of ground on the cluster connector to be specific the 4th term down on the passenger side. Those very thin copper contacts.
The reason the water temp gauge is working is it has its own ground on the drivers side of that connector.
The other gauges are grounding through the instrument lights sockets until the headlights are turned on and 12 volts is sent to the inst lights breaking the ground.
OK now let the fun begin !!!
I don't buy the headlight grounding bracket as the cause because that bracket only does 1 thing, it provides a ground for the white wire side of the courtesy lights so turning the **** can turn on the courtesy lights.
IMO you guys are faulting the headlight switch when the problem is the lack of ground on the cluster connector to be specific the 4th term down on the passenger side. Those very thin copper contacts.
The reason the water temp gauge is working is it has its own ground on the drivers side of that connector.
The other gauges are grounding through the instrument lights sockets until the headlights are turned on and 12 volts is sent to the inst lights breaking the ground.
OK now let the fun begin !!!
Thread Starter
Racer
Joined: Feb 2001
Posts: 315
Likes: 0
From: Pensacola Florida
Thanks guys for all the great replies and photo.
I think I installed the switch grounding bracket.
I guess I will have to tear everything apart and start from scratch.
I am pretty much a novice when it comes to car repair!!
Thanks again.
Larry
I think I installed the switch grounding bracket.
I guess I will have to tear everything apart and start from scratch.
I am pretty much a novice when it comes to car repair!!
Thanks again.
Larry
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Larry to start just remove the center cluster and check the 12 wire connector on the back where it goes in. I hope you find one of the thin contacts folded over and not making contact. I can shoot you a pic if you need one.
(You could also just swing the cluster down and temp ground the metal housing and see if that fixes it.)
(You could also just swing the cluster down and temp ground the metal housing and see if that fixes it.)
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Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,847
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Larry,
This picture will show you what terminal power what!
This picture will show you what terminal power what!
Last edited by Willcox Corvette; Feb 7, 2010 at 03:16 PM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
Hey, Roger's educated 'guess' is as good as anyone's right now. If you think you may have "lost" ground to the gauge bezel, you can always just run a jumper wire from a known good ground point to a metal area on the bezel [that is supposed to be grounded]. If that makes the system work correctly, then you need to repair/replace/add the ground to the bezel. At least, that's simple to try and may negate having to pull the bezel again...if you luck out.