My '81 electrical problem
Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
My '81 electrical problem
My '81 has come-down with an electrical problem with the instruments and none of them are working now. The illumination in both speedo/tach and center gauges work fine, but nothing else is. The battery / alternator and the choke lites are both illuminated.
Checked the gauges fuse - it was good.
I removed the center gauges and made sure the connector was in place and tried again, but nothing.
Just thought I would ask if anyone has a hint as where I should look first. I thought it might be the instrument ground, but since the illumination lites come on, plus I did nothing to it....at least not intentionally anyways...I think the ground connection is good.
Trying to figure-out what is common between the tach, choke, and all the center gauges...??
Appreciate any leads.
Checked the gauges fuse - it was good.
I removed the center gauges and made sure the connector was in place and tried again, but nothing.
Just thought I would ask if anyone has a hint as where I should look first. I thought it might be the instrument ground, but since the illumination lites come on, plus I did nothing to it....at least not intentionally anyways...I think the ground connection is good.
Trying to figure-out what is common between the tach, choke, and all the center gauges...??
Appreciate any leads.
Last edited by LannyL81; Jul 3, 2014 at 07:38 AM.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,852
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Its unlikely a ground issue since the gauges don't use a common ground. You can trace the grounds in the picture below.
The gauges all pick up power on the second wire from the top in the connector. When you had this out did you check it for 12 volts? Are you sure the pcb is okay? As the pcb's age the fingers will tend to come loose and not make contact. If you checked the gauges fuse and you have power and you don't have power in the connector your going to have to find the break.
In regards to the fuse.. there are two cut inlets for voltage testing in the top. If you test on the left and then on the right that is not a guarantee that voltage is making it to the wire. If you have power on both test cut outs on the fuse... Pull the fuse and see if there is corrosion on the right side terminals. You can clean this with a small point file or some ridged sand paper.
There is nothing in common with the check engine light. If you look below, you will see power and ground to that lamp are from a different circuit.
Willcox
The gauges all pick up power on the second wire from the top in the connector. When you had this out did you check it for 12 volts? Are you sure the pcb is okay? As the pcb's age the fingers will tend to come loose and not make contact. If you checked the gauges fuse and you have power and you don't have power in the connector your going to have to find the break.
In regards to the fuse.. there are two cut inlets for voltage testing in the top. If you test on the left and then on the right that is not a guarantee that voltage is making it to the wire. If you have power on both test cut outs on the fuse... Pull the fuse and see if there is corrosion on the right side terminals. You can clean this with a small point file or some ridged sand paper.
There is nothing in common with the check engine light. If you look below, you will see power and ground to that lamp are from a different circuit.
Willcox
Last edited by Willcox Corvette; Jul 2, 2014 at 11:35 PM.
Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
Thanks for the replies:
I did check the gauges fuse and it was good.
According to the manual the illumination lamps use the same instrument ground as the gauges....but will of course check further into this.
The Check Engine Lite is not on, the Choke lamp in the speedo / tach and then the Battery lamp in the center gauges are both on.
Put a new flex circuit on the center gauges; the speedo/tach is nearing replacement though.
Sure sounds like a ground connection is missing.....guess I will have to take the speedo / tach assembly out....again...... to get to the instrument ground connection.
I did check the gauges fuse and it was good.
According to the manual the illumination lamps use the same instrument ground as the gauges....but will of course check further into this.
The Check Engine Lite is not on, the Choke lamp in the speedo / tach and then the Battery lamp in the center gauges are both on.
Put a new flex circuit on the center gauges; the speedo/tach is nearing replacement though.
Sure sounds like a ground connection is missing.....guess I will have to take the speedo / tach assembly out....again...... to get to the instrument ground connection.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,852
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Larry-
about the only way for that to happen would be if something else was chasing a ground (ie: Headlamp switch). You could prove this by pulling the center dash and testing the grounds on the 150 circuit for voltage. Then unplug the headlamp switch and see if it goes away. This circuit is the ground on the top right, and the forth wire down on left side of the schematic above.
I just looked at the schematic on this... and the gauges use a separate finger on the pcb, but they all go back to circuit 150.(dash ground). This ground is located on the inside of the A Pillar...
about the only way for that to happen would be if something else was chasing a ground (ie: Headlamp switch). You could prove this by pulling the center dash and testing the grounds on the 150 circuit for voltage. Then unplug the headlamp switch and see if it goes away. This circuit is the ground on the top right, and the forth wire down on left side of the schematic above.
I just looked at the schematic on this... and the gauges use a separate finger on the pcb, but they all go back to circuit 150.(dash ground). This ground is located on the inside of the A Pillar...
Last edited by Willcox Corvette; Jul 3, 2014 at 10:37 PM.
Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
YEP....that ground on the inside of the A pillar, the so called "Instrument Panel ground"is the one I am going after. Perhaps I broke a wire when I re-installed the dash or something. Going to be working on this Saturday morning.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,852
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Take a look at it.. if the wire isn't broke.. I'd remove the bolt, clean both surfaces. But.. I had a 79 a long time ago... the ground at the number 1 body mount was corroded and every time I turned on the headlamps the center dash gauges would turn off.. The issue was the ground, the headlamp switch was looking for a ground and it took the path of least resistance... thus my comment about the headlamp switch.
The 79 had all kinds of electrical issues, it was a burn/rebuild car.. (another lesson learned at a much younger age)... Never buy a burned car to fix...
I hope you find it, I'll have my cell with me tomorrow and check back in.. won't be able to answer you till evening though.
Willcox
The 79 had all kinds of electrical issues, it was a burn/rebuild car.. (another lesson learned at a much younger age)... Never buy a burned car to fix...
I hope you find it, I'll have my cell with me tomorrow and check back in.. won't be able to answer you till evening though.
Willcox
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Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
SOLVED:
Problem was pretty much due to myself mis-reading the fuse panel and the location of the Gauges fuse. Apparently I was checking the wrong fuse all along.....AAARRRGGGHHHH.
Also it appears that my DMM is a bit flakey as I getting resistance between gnd connections which should have been zero ohms; I was reading 2 - 4 ohms, sometimes as much as 10 ohms.
Anyways I just began to pull every fuse I could get to and found a 20A blown. Replaced it and now have voltage to all gauges.....YEAH!!! I did find that I needed to clean all the contacts of both speedo/tach and center gauges as they were not making a really good connections.....so it was not a complete waste of time in taking everything apart...AGAIN....
Bottom line....problem solved....putting it back together and continuing-on with the re-assembly. After the gauges are in, next will be the door weatherstripping.
Thanks to everyone and especially Willcox Corvette for the flex circuit pin-out...saved that one.
Back to work.
LannyL81
Problem was pretty much due to myself mis-reading the fuse panel and the location of the Gauges fuse. Apparently I was checking the wrong fuse all along.....AAARRRGGGHHHH.
Also it appears that my DMM is a bit flakey as I getting resistance between gnd connections which should have been zero ohms; I was reading 2 - 4 ohms, sometimes as much as 10 ohms.
Anyways I just began to pull every fuse I could get to and found a 20A blown. Replaced it and now have voltage to all gauges.....YEAH!!! I did find that I needed to clean all the contacts of both speedo/tach and center gauges as they were not making a really good connections.....so it was not a complete waste of time in taking everything apart...AGAIN....
Bottom line....problem solved....putting it back together and continuing-on with the re-assembly. After the gauges are in, next will be the door weatherstripping.
Thanks to everyone and especially Willcox Corvette for the flex circuit pin-out...saved that one.
Back to work.
LannyL81
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,852
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
good deal Larry.. 
Glad you got it fixed
You should search the tech pictures side of the site... you can search it by year and there are tons of pictures that may help you out. They are free to anyone!
Willcox
Glad you got it fixed You should search the tech pictures side of the site... you can search it by year and there are tons of pictures that may help you out. They are free to anyone!
Willcox
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,852
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Nice.. Hope I can get all of them on there soon. I have a couple of thousand more to add, just no time. We're working in the site right now trying to upgrade some stuff. Hopefully when we are done we can get it finished. For now as I post them I add them.
Willcox
Willcox