Electrical issue fuel and temp gauge

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roadblock69

roadblock69

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My 1969 Dart Custom is experiencing an electrical gremlin. It doesnt happen all the time but here is what its doing. First: 100% bone stock 318 2bbl 904 auto. Every so often the fuel gauge will peg out way past the full line. The temp gauge also follows along showing a reading that is actually hotter than the motor temp. Over the summer it got a little scary. I realized there was an electrical issue when i turned on the left directional and the gauges went back to their normal position. My question to the forum members would be: Any idea what the cause would be without just changing parts randomly?
 
The voltage regulator for the two guages would be my first thought.
Way past full on the fuel guage would lead me to think that the regulator is giving the guages a full 12 volts instead of the pulsed 5 volts they normally run on.
Some have it on the back of the cluster, and some have it inside one of the guages.
I don't know which years had which though, but there is a member on here that rebuilds them if needed.
 
This problem will ruin your gauges if not corrected. The left turn signal factor may be just coincidence or may be clue that the problem is in the wiring harness.
After 45 years, chaffing through wire casings is a possibility.
Failing instrument voltage regulator is the most common cause of wild needle swings though so I would start there.
 
Cheap and easy to replace your old thermo-electric dash Vreg with a modern electronic one. $30 on ebay. Search "voltage limiter".
 
Back to the same problem again. I changed the voltage reducer on the back of the cluster. The problem seemed to go away for a while. Later in the fall it reappeared again sporadically. Since then I have changed the alternator and the voltage regulator. I still have the same problem of te gauges pegging. If I unplug the temp sending unit the temp gauge falls to zero. the voltage reducer was warranteed so I ordered another one today. Any other suggestions besides the ivr? I tested the one that put in last summer it appeared to be 'open'. My only other thought was that the old alternator would sometimes overcharge and could have cooked it.
 
I've preached and preached this. You guys MUST start thinking of things as a SYSTEM end to end, visualize the entire path in your mind, and what connectors and problem areas you can have?

In my case there were several

The three or 4 things I can think of for your case in no particular order:

IVR socket: On my cluster, the brass springy contact fingers were NOT making contact with the PC board. One of these is ground, and would cause this. I had to solder jumpers across the contacts to the board

(In my case, I abandoned the original connectors. The additional wires you see here are, black, ground pigtails, and blue / white, switched 12V to the IVR)

Additionally, the "new" IVR could be defective. Just because you replaced it does not mean it's good

(What kind of IVR did you buy, IE a "parts store" thing, used / junkyard, or RTE solid state, etc?)

The gauge unit could have internal problems

Unlikely, but possible, is a pinched area in the harness allowing the sender wire to short to ground.

http://www.forabodiesonly.com/mopar/showthread.php?p=1970209465

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Is it possible that a ground to short on the fuel guage could also cause the temp guage to react?
(Could it actually be the fuel sender causing it?)

I can't think of how, but they are on the same power circuit.
 
Don't know. The left signal wire and sender wire ( all the rear harness wires ) are exposed inside the trunk just enough to be beat up, chaffed, etc...
They are all in the same connector behind the left kick panel too.
69 model has a metal harness strap above the instrument cluster that makes a sore spot too.
Just places where I would start hunting the problem.
 
roadblock69 said:
the fuel gauge will peg ................... The temp gauge also follows along showing a reading that is actually hotter than the motor temp.
Click to expand...

Somehow I missed this connection

I would concentrate on the spring contacts as I mentioned for the IVR and suspect the IVR itself. If you do NOT have a solid state IVR, get one.

Something else you should do if you have not, but which will not cause this, is to solder / repair the PC board pins, and replace the nuts on the gauge studs. loosen/ tighten the nuts a few times to "scrub" the connection clean. Provide a ground pigtail on the cluster if you have not.
 
Thanks for the replies. What do you mean by a ground pigtail? Im a little weak on wiring unfortunately. The IVR was a made by Wells if that makes a difference
 
roadblock69 said:
Thanks for the replies. What do you mean by a ground pigtail? Im a little weak on wiring unfortunately. The IVR was a made by Wells if that makes a difference
Click to expand...

Del means find a good solid ground surface on your cluster board and run a wire from it to a good body ground, so it won't have to rely on sheet metal screws for a good ground.

I really think this and the pin connections may do it.
 
I changed the IVR with the parts store replacement. No change in how the gauges are functioning. The new IVR came with a stud to ground the unit. I tried grounding that too. Checked the nuts on the back of the gauges by loosening them and tightening them back up a few times. Cleaned and tightened the motor to firewall ground. Checked the bulkhead connections which were clean and tight. Short of pulling the cluster out and checking the spring clamps that hold the IVR i am stumped. Im planning on getting some aftermarket gauges for the summer and running them until i can sort out the factory gauge issue. anyone have any suggestions which brand and model to get for fuel temp and oil? I will mount them under the ashtray.
 
I have changed the printed circuit boards and voltage limiter with parts from Classic Industries. Checked and cleaned the gas tank sending unit strap. Changed the engine to firewall ground. Checked all the bulkhead connections.
When I finished the circuit boards I did notice the spring clips were loose. All the dash lights work now as well as the directional arrows which didn't work before. The fuel and temp gauge spiked to full/hot once and then dropped off to where the should have been or thereabouts. Then they dropped back off to zero. What am I missing? Any suggestions?
 
This is indeed getting to be troubling. At this point, I just don't know. Did you add a ground wire to the cluster?

Check your charging voltage. Run the car, get up to temp, and get the battery "normalized" after starting. You still run an ammeter? Does it run "normally" IE most of the time near center?
 
I did check the voltage a while back and it was good. I cant recall the exact numbers now. I tried a ground wire from a screw that holds the cluster to the bezel. That didn't change anything. I was pretty excited when the gauges stayed where they were supposed to be for 3-4 minutes!! The ammeter runs in the normal range.
 
roadblock69 said:
I have changed the printed circuit boards and voltage limiter with parts from Classic Industries. Checked and cleaned the gas tank sending unit strap. Changed the engine to firewall ground. Checked all the bulkhead connections.
When I finished the circuit boards I did notice the spring clips were loose. All the dash lights work now as well as the directional arrows which didn't work before. The fuel and temp gauge spiked to full/hot once and then dropped off to where the should have been or thereabouts. Then they dropped back off to zero. What am I missing? Any suggestions?
Click to expand...

This reads like your aftermarket regulator is/was defective.
 
I would agree but the odds would be against it. The parts store one was tried and then returned for another one. I bought another from Classic Industries too and no luck. So all in all that would be three IVR's.
 
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