79 Gauge Electrical Problem
Thread Starter
Instructor
Joined: Jun 2009
Posts: 155
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From: Minnesota
79 Gauge Electrical Problem
I am by no means a car guy. I picked up a 79 Corvette Coupe on April 1st and have been doing small things to it. Replacing the Radio, Power Steering Valve and Lines, etc...
I have a problem with my center dash gauges. Someone who has previously owned this must have done some electrical work since if I turn the lights on and the light gauges themselves are enabled (Via the light rheostat) the power is lost to the center gauges (Fuel, Temp, Clock, etc...). All gauges immediately die. I believe the problem is just the power to the gauges must be terminated at the light rheostat. Once the power is enabled the power to the gauges is no longer available.
I picked up a wiring diagram but it didn't really help.
2 Questions:
1) I need to try and figure out where the power for the gauges should be terminated to and (If anyone knows) what color the wire sheath for the power on the harness is.
2) Since I have never worked on a Corvettes dash wiring I'm wondering how can I get at it? Do I have to take the dash out or can I just get at it from underneath?
Any and all help is appreciated
Thanks in Advance
Paul
I have a problem with my center dash gauges. Someone who has previously owned this must have done some electrical work since if I turn the lights on and the light gauges themselves are enabled (Via the light rheostat) the power is lost to the center gauges (Fuel, Temp, Clock, etc...). All gauges immediately die. I believe the problem is just the power to the gauges must be terminated at the light rheostat. Once the power is enabled the power to the gauges is no longer available.
I picked up a wiring diagram but it didn't really help.
2 Questions:
1) I need to try and figure out where the power for the gauges should be terminated to and (If anyone knows) what color the wire sheath for the power on the harness is.
2) Since I have never worked on a Corvettes dash wiring I'm wondering how can I get at it? Do I have to take the dash out or can I just get at it from underneath?
Any and all help is appreciated
Thanks in Advance
Paul
Le Mans Master
Joined: Mar 2001
Posts: 6,640
Likes: 287
From: Ann Arbor Michigan
Power comes from the "Gages" fuse and the wire color is pink with black stripe.
Gary
http://www.corvetteforum.net/c3/tune.../index18.shtml
Gary
http://www.corvetteforum.net/c3/tune.../index18.shtml
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
If the gauges work until you turn on the lights, it's very possible the lights are using all the capacity of the ground to the cluster, or the gauges are grounding thru the bulbs. Either way, it's a ground problem to the cluster. Fix that and you cure your problem.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
Thread Starter
Instructor
Joined: Jun 2009
Posts: 155
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From: Minnesota
I put in a radio earlier this spring and I recall the mylar circuit board was partially modified. At least one of the coppers runs was cut off. I'm guessing it had to do with the seat belt alarm and the contacts were getting warped. Do you think that there is any possible connection with this?
How would you suggest I look for a ground problem? Are you suggesting I have a tarnished/rusted connection? Could you give some tips on what I should do to look for this, since it is working I am unclear as to how to start to troublwshoot.
Thx
How would you suggest I look for a ground problem? Are you suggesting I have a tarnished/rusted connection? Could you give some tips on what I should do to look for this, since it is working I am unclear as to how to start to troublwshoot.
Thx
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
First thing you need is a wiring diagram for your car or the FSM. There are a couple of grounds under the console, and another one on the cage just over the hood release handle.
The printed circuit is a common failure- they get old. My 77 has a contact (clock power) that's toast. I jumpered around it.
FWIW- the gauges power feed is as Duke says- pink/black. All the instrument lights are gray, radio power is yellow, and all the grounds are black. Oil pressure is blue, water temp green and fuel gauge is tan. Off the top of my coconut, so double check.
The printed circuit is a common failure- they get old. My 77 has a contact (clock power) that's toast. I jumpered around it.
FWIW- the gauges power feed is as Duke says- pink/black. All the instrument lights are gray, radio power is yellow, and all the grounds are black. Oil pressure is blue, water temp green and fuel gauge is tan. Off the top of my coconut, so double check.
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Thread Starter
Instructor
Joined: Jun 2009
Posts: 155
Likes: 0
From: Minnesota
Electrical Grounds
I did pick up a wiring diagram but it doesn't appear to me to be very effective. I actaully have an electronic tech degree (AD) but haven't done much since the early eighties. The diagram is so dog gone compressed it is hard to read, it is the original GM document in mylar.
I will order the printed circuit board and replace it and when I am inside I will look at the harness and attempt to follow the wire back to the grounds.
For some reason the Tach went goofy (It just pegged) for a few minutes today as well, so I do want to get on this but it will probably take a couple of weeks in getting the parts and the time. Took me a few times of battery off and on to get the Tach to come back.
I appreciate everyones time to give me the help!!!
Paul
I will order the printed circuit board and replace it and when I am inside I will look at the harness and attempt to follow the wire back to the grounds.
For some reason the Tach went goofy (It just pegged) for a few minutes today as well, so I do want to get on this but it will probably take a couple of weeks in getting the parts and the time. Took me a few times of battery off and on to get the Tach to come back.
I appreciate everyones time to give me the help!!!
Paul
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
I have a .pdf file for my 77. It's not excatly the same as your 79, but I bet it'll be close enough to find your grounds.
PM me your email and I'll send it to you. (It's easier to read than the one you have even if it's not exactly correct)
PM me your email and I'll send it to you. (It's easier to read than the one you have even if it's not exactly correct)
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
also make sure that plug for circuit board is plugged in good. mine has worked loose before after radio install, and i had to clean the connectors.
http://www.corvetteforum.net/c3/tune.../index18.shtml
http://www.corvetteforum.net/c3/tune.../index18.shtml
Thread Starter
Instructor
Joined: Jun 2009
Posts: 155
Likes: 0
From: Minnesota
All Fixed - :-)
Well after replacing the circuit board most of the problems went away. The only thing left that is annoying is the generator light is always on and I don't see anything wrong with it. It is charging everything up well, so i am stumped on that.
Anyways thanks to everyone for the assistance.
Paul
Anyways thanks to everyone for the assistance.
Paul
