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Instrument Panel Trouble
https://slantsix.org/forum/viewtopic.php?t=48692		 Page 1 of 1
Author:  R. Wood [ Tue May 01, 2012 11:21 am ]
Post subject:  Instrument Panel Trouble
1975 Valiant

I've got a dead gas gauge and temp gauge. Also the instrument panel turn signals (green arrows) are working intermittantly (actual signals working correctly). Ammeter and other bulbs are working corectly.

Here's what I've done so far:
Solid State voltage regulator - 7508 - tested on bench with 12VDC input, got 4.98VDC output.
Cleaned all copper traces, especially where the four nuts behind the two bad gauges tighten down on the circuit board
Bench-checked all bulbs, replaced a couple bad sockets
Cleaned off ground strap that jumpers over the rubber fuel line at the gas tank. Brushed connectors there.

What should I do next? Is it possible that I have a bad pin or two on the octal power supply harness that connects to the back the panel?

Thanks for the help,


Richard
Author:  SlantSixDan [ Tue May 01, 2012 2:09 pm ]
Post subject: 
If the original ICVR failed by the points sticking closed (50/50 odds whether it fails this way or stuck open), then the fuel and temp gauges themselves will have been cooked to death.

Bad pin on back of instrument cluster is less likely than spread socket on octal socket at top end of wires.
Author:  R. Wood [ Tue May 01, 2012 3:49 pm ]
Post subject: 
Thanks for the reply, Dan. Is there a source for those gauges or a workaround? I'm wondering what my options are.
Author:  Nongan [ Tue May 01, 2012 3:52 pm ]
Post subject: 
I think I have a set of them from my 74, if they are the same I will cut you a deal on them, if they are dead.
Author:  DusterIdiot [ Tue May 01, 2012 6:11 pm ]
Post subject:  Yep...
Quote:
I think I have a set of them from my 74, if they are the same I will cut you a deal on them, if they are dead.

The 74 cluster can be swapped for the 1975 cluster, the only thing he won't have is the EGR light in the 1974 cluster...gauges are the same
for those years as well.

-D.Idiot
Author:  SlantSixDan [ Tue May 01, 2012 6:58 pm ]
Post subject: 
Interchange on the fuel and temp gauges is '72-'76 Valiant, Duster, Dart. Interchange on the ammeter is '72-'75 Valiant, Duster, Dart.
Author:  R. Wood [ Tue May 01, 2012 9:04 pm ]
Post subject: 
Thanks. Nongan, I will PM you.

What is the procedure for testing a fuel and a tempo gauge? I'd like to be sure the ones I remove are actually dead, and would like to test the ones I put back in there. I assume I'd remove the PC board from the back of the cluster.
Author:  SlantSixDan [ Tue May 01, 2012 9:08 pm ]
Post subject: 
Hit 'em briefly with a regular household 9v battery. If the needles move, they're not burned out (though you need a special tester or a factory service manual and some resistors and a benchtop power supply to determine if their calibration's reasonably accurate.)
Author:  R. Wood [ Sat Jun 09, 2012 7:01 pm ]
Post subject: 
An update on this. The gauge needles do start to climb when I connect them for a few sec to a 9V battery. I did, however, acquire, another instrument panel. I tested it's gauges, got the same result, and installed my voltage limiter from the old panel to the new. Put everything back together and the temp and fuel still do not work. They don't budge at all. :?

I read the FSM but I do not have the referenced test tool to carry out its procedures (although I imagine that tool is not hard to make if there is a schematic available).

I think I have my voltage regulator wired right but I post a pic here in case something jumps out as wrong. I used the tabs from the original one as terminals for the new input and output.

Not sure where to focus next - I was thinking of putting test leads on the fuel gauge terminals so I can check voltage while it is in the actual circuit. Or perhaps I should look at the sending unit end. I don't know if the fuel and temp gauges are each failing for a common reason or for separate reasons.

On the bright side, the dash turn signals are no longer intermittent and I took the opportunity to apply Dan's Special Speedometer Cable Sauce. Nice and smooth now. And with the new panel my car has 51K miles on it instead of 92K!

Here's the voltage limiter:

Image
Author:  DusterIdiot [ Sat Jun 09, 2012 7:50 pm ]
Post subject:  Like the wire crawls...
If testing a gas gauge, get a buddy to spot for you at the drivers wheel and turn the key to 'on'/not 'start', and pull the sending wire off the sender and ground it for a second or two, if the gauge does not climb (we know the gauge works), then you have some wiring to trace down...If it does climb, maybe check to make sure the sender has it's ground strap.

I'd bet the temp sending wire either has become brittle, or possibly the bulkhead connector is not in good shape any more.

-D.Idiot
Author:  R. Wood [ Sun Jun 10, 2012 8:37 pm ]
Post subject:  It's Alive
Thanks for the info; this did lead to the fix.

The gauge did not climb, and the reason is both embarrassing and relieving at the same time. I was about to get really confused by the bulkhead configuration (apparently I have the wrong FSM for this) when I noticed that in Cavity Six of the fuse box there's a fuse that serves only the gauges in question, and the voltage regulator that serves them. I had already checked the fuse, and I did once again with an ohmmeter - still good. But I noticed that one end of the fuse was not seated all the way, and between that and some oxidation on the clip, it was not passing current. Popped that back in place and back in business.

So I went the long way around the barn on this one; doubtful I'm not the first or last who could have fixed something without even having to buy parts. I did learn a lot about how the circuit works, though, and I now have a new solid state VR as well as a happier speedometer.

Thanks for the assistance! Now to figure out why the horn's not working...... 8)
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