johngammel

This is what I know. With all the wiring connected and probably about 1/2 of a tank of gas the "fuel" gauge is at "E" with the ignition turned on. The ohms to ground at the sending unit is near zero. With the brown wire removed from the tank sending unit there is about 18.5 ohms measured to ground. With the brown wire removed from the gauge it rapidly goes to "F". With both ends of what is apparently the fuel gauge wire removed the resistance to ground at the ring terminal is zero - which seems to be very bad. With a temporary wire connected from the sender to the back of the gauge it reads right at 1/2. I'm lead to the conclusion that the brown wire is shorted somewhere in the new harness.

It seems the best course of action is just to run a parallel brown wire to keep the color coding correct and tape it to the existing harness. Unless a judge is going to remove the cover from the gas tank cover no one will even know.

Thoughts?

TheCar

It sounds like you have a good handle on the problem. Overlaying the harness Is a good idea, but If you are feeling lucky pick a spot in the middle remove some tape and cut the brown wire, then you can measure forward and back to find out where it's shorted, then decide if you want to chase it further, at least you won't have to run a wire all the way. If your lucky you might even find it. Check near splices, turn outs and connectors, you may have a mispinned connector if it goes through one. You will be doing a lot of taping the other way.

johngammel

That's the process the navy used in the 60s - I called it "divide and conquer".

I've done a physical check of the harness and don't see anyway damage. Since it's new my guess is that they just check for continuity and the problem won't show up until it's actually in the car. Oh well - I'll just continue plugging along.

jimh_1962

If you want to rule it out then bench test the gauge and sending unit out of the car. Also check the gauge housing for any grounding problems.

I figured that one out (replaced my fuel sending unit and figured out the original one was good). Paint was preventing a good ground on the housing. Finally, decided to pull both gauge and sending unit. To check to see what was going on. Sure enough the paint I had used on the tabs on the housing was preventing a good ground.

Frankie the Fink

Every C1 owner should run the add'l ground from the sending unit to the frame to avoid future feedback from the brake light circuits -- a common C1 problem known as "The Dancing Fuel Gauge".

This JohnZ article tells you how to do that and also how to check out the fuel gauge/sending unit...

jimh_1962

Yeah, that was the first thing I did with the ground on the sender. In my case, it was all in the grounding in the gauge housing. I would take it out and test everything on a bench since it is easy to do. Just need a 12 DC volt power supply. Cheap and handy... I made my own out of a computer power supply.

ejboyd5

I'm not sure if this means you have checked the continuity of the brown wire from end to end or have not. If not, that would be my first test. If the results show a break, I would connect a pulse generator to one end of the brown wire and check at several locations along the run to see where the signal ends. By the way, my bet is on a poor connection rather than a fault in a new harness - let us know.