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I'm having the usual trouble with aftermarket fuel sending units on my 1966 Mustang. I cleaned up my original, and it also isn't reading accurate. Out of the tank, I can get the repro. sending unit to move the gauge, but the original doesn't, although it passes the "ohms test".
Does anyone know a place that can restore an original fuel sending unit?
 

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I don't. I can't help you with finding a source for sending unit restoration.

However, I hope you don't mind me picking at your problem. As I understand you, you say that the original passes the "ohms test" but "it also isn't reading accurate":

When you put one side of your multimeter on the lug and the other on the flange, do you get about 70 ohms in the "empty" arm position, and around 10 ohms in the "full" arm position? If so, then you are getting a good signal out of it. That sending unit just might be perfectly good.

There are four other items in your circuit that affect your reading: the sending unit wire resistance (between the lug and the gauge), the gauge itself, the Instrument Voltage Regulator (IVR) operation, and the IVR ground. ANY of those influence your gauge accuracy.

For around $10 you can get a solid state voltage regulator that you can dial to 5v output. Swapping this out with your IVR can prove whether or not this component is the problem. My sending unit wire had about 6 ohms resistance (I thought it was on the high side) but also has continuity, so I knew that this isn't my problem. Are you sure that you have a really good connection at the lug? I think you have good IVR ground since one sending unit operates the gauge correctly but the other doesn't. However, I'm not so sure about your old sending unit grounding. Have you checked good grounding at the sending unit?
 

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Bob's Speedometer is in Michigan and they restore them. I've never dealt with them just emailed them about restoring a fuel sender. I emailed another shop in northern Ohio but they did not respond. I can't find that email or remember the name of the shop. Good luck. Dave .
 
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