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42Ford M-H

42Ford M-H

Senior Member
Well I rearranged my tail light wiring, went to drive the truck and found I had no low beams. High beams works. And my gas gauge stopped working. Found a bare connector resting on the frame where I had moved the tail light wiring. Looks like I blew both headlights.

Some quick testing of my sending unit showed no change in resistance. It’s still in the tank, But i got nothing on my meter. Does it seem possible that the wire shorting on the frame toasted the sending unit or is it just extremely weird timing? Are these sending units fixable? I haven’t searched yet, but is their an easy way to test the gas gauge?
 
If it is an original sending unit it does not work in a manor that would show a resistance change. It provides a ground path to the gauge and controls the current flow to ground by pulsing a set of points. I would think it odd that shorted wire in a different circuit would damage the sender.
Sounds like there could be some wiring issues including possible grounding errors.
 
What Seery said about grounding path for the gauge rings a bell for me. I remember being told that you could test the dash unit by grounding the sending wire, but was cautioned to not let it stay on ground or it would burn out the gauge. In any case, don't try replacing the tank sending unit with modern, as they don't work with the original gauges.

The headlight hi beam issue sounds like a dimmer switch issue. Those buggers have a repiutationfor going south.
 
I took the old bulb out and checked voltage. Then swapped in another bulb I had laying around. Worked on both high and low beams. Just seems weird both bulbs and gas gauge stopped working at the same time. And that was right after I moved those wires. I'm really leaning towards that wire shorting out on the frame is the cause. Any other way to test fuel gauge other that briefly touching sending unit wire to positive ground?


found another thread with info to try testing the gauge.
https://www.ford-trucks.com/forums/979251-fuel-gauge-doesnt-work.html
 
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Many electrical problems are caused by old "bullet" connecters somewhere in the circuit. We remove the old connector and solder the wires, and cover the splice with a piece of heat shrink tubing to make it look "real". The other common problem is lack of adequate ground. Years of dirt and rust make the chassis a poor conductor. We add a separate ground wire to all devices, and make sure the ground is good using an ohmmeter. As for the fuel sender, the original King Seely senders are now replaced with a variable resistor operated by the float. Properly grounding the mounting flange, and calibrating the reading by bending the float arm can approximate the amount of fuel in the tank. Most gauges will operate with the resistor. I have one in my '47, and it works fine.
 
supereal said:
Many electrical problems are caused by old "bullet" connecters somewhere in the circuit. We remove the old connector and solder the wires, and cover the splice with a piece of heat shrink tubing to make it look "real". The other common problem is lack of adequate ground. Years of dirt and rust make the chassis a poor conductor. We add a separate ground wire to all devices, and make sure the ground is good using an ohmmeter. As for the fuel sender, the original King Seely senders are now replaced with a variable resistor operated by the float. Properly grounding the mounting flange, and calibrating the reading by bending the float arm can approximate the amount of fuel in the tank. Most gauges will operate with the resistor. I have one in my '47, and it works fine.
Click to expand...

Bob, I'm reminded by your post that yes, the modern senders do work with original gauges, but no, they don't work nearly as well as the original due to the different systems, providing a considerably less that full sweep of the gauge needle.
 
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