Gauges driving me crazy

[Dmac620]

I recently picked up a 1959 Ford Ranch wagon. I do not have a working fuel or temperature gauge. When I purchased it, the fuel gauge would read 1/4 tank no matter what level of fuel was in the tank, full to drained and completely empty. When I would start the car, the temperature gauge would immediately climb to the “H” and pin itself to the right side. I tested the constant voltage regulator on the back of the gauge panel and found that both terminals on the regulator were reading just over 13 volts when the car was running. Clearly, the regulator was not dropping the feed to the gauges down to the desired 5 volt range. I swapped out the regulator and now I get zero readings on both the fuel and temperature gauges. I tested the terminals on the renew regulator and found 13.2 volts going in and 5.06 volts going out to the gauges. I then tested the volts on each power terminal going into each gauge and at normal engine operating temperature. The power feed going into the temp gauge reads 5.03 volts and the terminal on the back of the gauge that is fed by the sender wire is reading 3.6 volts. Seems like the resistor in the sender is doing its job. The power feed going into the fuel gauge reads 5.03 volts and the sender terminal reads 4.7 volts. (Tank was filled approximately 25 miles ago so it is nearly full)
Additional tests I did.... I removed each gauge from the panel and tested it independently by attaching the positive side of a 3 volt battery to one terminal and the negative side to the other terminal. When I did this to the fuel gauge it read 3/4 full. When done to the temp gauge, it read just under the hot “H” mark. Therefore, both gauges are working. I removed the wire going to the temp sending unit on the engine and grounded it and the temp gauge immediately climbed to the “H”. I swapped two different temp sending units into the engine block and reattached the wire and both rendered no reading on the gauge. Lastly, I removed the sender line going into the fuel gauge while it is running and nothing happens to the gauge, still reads completely empty.
I’m at wits end.... not sure where to look now to diagnose. A ground somewhere? I found a separate ground wire run from the back of the gauge panel to the bottom of dash that was there when I purchased the car. I undid it and saw no change at the gauges.
Any advice is GREATLY appreciated.

[fordor41]

temp gauge, try running a new temporary wire from gauge to sender. sound like sender wire may be grounded somewhere. wires get pretty brittle on top of the engine. fuel sender may be stuck, or just plain bad,. ground the sender wire at the fuel sender. gauge should read full. also try grounding he fuel sender to the frame

[Daves55Sedan]

I agree with fordor41. Sounds to me like wire insulation for the temp sending unit is broken off somewhere.
Get a long piece of 14ga or 16ga wire to reach from the sender to the guage and connect test alligator clips to the ends. Disconnect both ends of original wire at guage and sender. Attach both ends of test wire with alligator clips and start the engine. If the guage is now working, install a new wire with ring tongue terminals and remove the old wire. Problem solved.
Ditto again what fordor 41 said about the fuel guage. It could be bad in which case it can probably be repaired by Bobs Speedometer or Williamsons Instruments, But before condemning it, try running a separate ground wire from the grounding screw on the firewall all the way back to the sending unit. Connect the wire to the sending unit with some sort of clamp (connection must be clean and rust free). Now start the engine and see if the fuel guage reads full. If so, all you needed was a good ground connection to the sender.

[54vicky]

no need to start the engine to test for ground.that would serve no purpose

[dmsfrr]

... also try grounding the fuel sender to the frame

Most electrical parts are grounded to the body, or the engine, not sure if the frame is part of an electrical circuit of most vehicles.

A while back Daves55 and I shared a brief conversation about how the heck did Ford intend for the fuel sender & tank to be grounded, because there is no apparent Ground connection for the fuel sender.

The sender grounds to the tank, but how is the tank grounded?
Apparently in his vehicles as well as my 2 oldies... the fuel tank is/was installed into the car with some variety of cushioning or insulating material between the tank and body, and also on the mounting straps that hold it to the car.

The possible answer we thought of... perhaps the sender & tank are grounded thru the steel fuel line that is clipped to the frame on the way to the engine compartment.??? But that might seem a bit sketchy...

The agreed conclusion was to install a dedicated ground wire from the fuel sender to the car body in a situation where the fuel gauge circuit was acting up, to eliminate it as a possible problem if nothing else.
.

[Daves55Sedan]

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Originally Posted by 54vicky

no need to start the engine to test for ground.that would serve no purpose

Don't care about testing ground. Want to see if the guage is working after new ground wire is hooked up.
Tell ya what. Just turn the key ON. No need to start engine to check if fuel guage is working.
But you do need to run the engine awhile to see if temp guage goes from Cold to about half way to Hot.

[Ford blue blood]

Every car I've built has had the tank grounded to the body and the body and chassis connected with a woven grounding strap. Every single "weird/makes no sense" electrical problem I have worked on has been grounding issues.