Bad Ground on my 67 Valiant Dash Cluster?

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jimmys67

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I have a 67 Valiant. The temp and amp gauges worked well until one day I took the cluster out to replace the dash lights. While testing the lights, (I had the engine running,) the gauges were up and down totally erratic. I turned the engine off, and then turned the key "on". The gauges never moved again. Obviously, I shorted something out. I've gone over the circuit board with a test light and ohm meter. I changed the voltage limiter. No help. One strange thing is, when I check the positive and neg posts on the circuit board, I'm showing 12 volt on pos and neg. I don't think that's right. Could this be my problem? Please help.
 
Sounds like a short somewhere. Did you short the cluster against the dash when you had it out?
 
Well, you could have just lost the ground lead to the cluster; it'll mess up all the gauge operations. Does the high beam indicator work? It has to have a ground at a cluster to work.
 
The black wire isn't a ground wire. There isn't a actual copper ground wire there. Nearly everything on these cars uses a daisy chain of parts and hardware for chassis ground.
Bottom line, Inst' panel aint gonna work right while dangling from its harness connectors.
 
Yes. I was disconnecting the black wire on the circuit board, and the wrench touched the metal part of the dash. It blew the fusible link under the hood. That seems pretty extreme for disconnecting a dash cluster.
 
jimmys67 said:
Yes. I was disconnecting the black wire on the circuit board, and the wrench touched the metal part of the dash. It blew the fusible link under the hood. That seems pretty extreme for disconnecting a dash cluster.
Click to expand...

It isn't extreme where a live ALT' amp gauge lives.
Most any service in the manual starts with "Remove negative battery terminal".
The manuals are free downloads too.
 
If you want, I have some parts clusters I can rob those gauges from. Did you fry the board? I have those too if you need that too.
 
You're right. Instructions always say "disconnect negative battery cable before proceeding". Sometimes, I have. Sometimes, (like now) I didn't. I got bit, and I think that I'll always disconnect the battery from now on.
It's kind of funny that you mention a "live alt amp gauge". All of the other gauges are reading a pulsating voltage with an ohms meter. The alt gauge is as dead as a door nail. I tightened all of the posts on the circuit board. Still dead. Don't know why. Maybe fried?
Another situation is, (and maybe because the cluster is out of the dash) the entire metal backside of the cluster is electrically alive. Even the casing of the voltage limiter is showing 12 volts. Maybe this is because the ground at the steering column is off.
Also, the gauges have the pulsating voltage when the key is off. When I turn the key on, but not running, I get 12 volts steady on all posts. Again, is this because of the steering column ground not being connected. ( I have the steering wheel lowered to remove the cluster.)
I'm confused. I hate, hate, hate, electrical problems. Any help you might offer would be really appreciated. Thank you, sir
 
It's pretty easy to tell if you ammeter is still working. If you have 12 volts on one terminal you should have it at the other one too. If one is dead then it's open (not likely though).
 
Which part of WV are you in? I am in western VA and may not be too far away.

MMM, yes the grounds have to be connected up for things to be working. The pulsing is normal but not with the key off. Buuuut with this last set of symptoms, I now suspect you have 12v shorted to the cluster ground. It is can be causing these symptoms by:
- When you have the key in RUN, there is 12v from the ignition switch being fed to the normal 12V input to the cluster; that puts 12v on the input of the limiter and with 12v on the ground side of the limiter due to the short, then the limiter does nothing.
- When you turn the key OFF, the 12v shorted to the cluster ground is putting 12v on the ground side of the limiter and the input of the limiter is near to ground due to other low circuits connected to the 12v ignition source 'pulling' it to ground. The limiter will then pulse; it does not care in which direction the current flows in its heating coil.

Try disconnecting/removing all of the instrument lamps and see what happens. Look at all of the nuts holding the circuti boards in place and make sure there are not washers overlapping and shorting any traces together.

Edit to add: Also remove both connectors and probe each one for 12v on each pin with the key off (with the neagtive of the meter on the chassis). There should not be 12v on any pin with the key off.
 
With the instrument panel dangling from its harness connectors a simple test lamp would show the entire housing as hot. That's the current attempting to use your test lamp as a ground.
If you want/need to continue testing in this manner, get a piece of wire with alligator clips both ends. Attach one end to inst' housing, the other end to bare metal such as column/pedal support and start testing over with your test lamp.
I think I said this before, a permanent dedicated ground wire is recommended.
 
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