just swapped out my corroded fuel sending unit and was thrilled to see my fuel gauge come back to life. unfortunately, it came back with a little too much life and is now reading far above the full mark on the gauge. did i mess up the grounding somehow on my reinstall? or is a potentially faulty aftermarket sending unit the culprit? i already took the unit out and checked the float, which seems to be operating as it should be. any ideas?

You will have better luck if you tell folks what year and model you are working on. A wagon and a sedan are not the same, and then there is the year differences.

I am going to assume you have an 85 to 88 since that is what I have worked on, those for sure have the internal float assembly and pickup pump. I do not have my Hayes or Bentley near right now, the advice will vary depending on the year.

The voltage should vary as you move the float up and down. You can check that with the unit out of the gas tank. Suggest you disconnect one side of the pick up pump and tape it up, you do not need that running all the time. Bad for the motor and not a good time for sparks you know. I would also be in a well vented area and have something to cover the tank opening. Keeps the junk that should not be in the tank out, and the fumes in.

Take your Volt Meter and measure the terminal at the top and put the negative lead to chassis. If the voltage does not change as the float moves up and down you either have the unit wired backwards somehow or the float is connected to the sending unit correctly. You should be able to verify the problem is fixed before you stick it back in the tank.

i'm working on a '91 244. just checked the ground, which seems good. when i disconnected the sending unit, the needle on the gas gauge floated downwards.

Hi there,

When you pinned the sender plug, did the black wire go to the yellow/red in the harness, and the gray to the gray? Does the tank pump work?

Also, look out for a bunch of aftermarket senders that got miswired. This photo shows what a miswired one looks like.


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Art Benstein near Baltimore

We childproofed our homes, but they are still getting in.

Hi Art,

Thanks for the info. I noticed that the wiring was a little different on the aftermarket part, but the location of + and - was also reversed on the new aftermarket pump I ordered. So the yellow wire is marked + and goes into the + terminal on the pump and the black wire is marked - and goes into the - terminal. Is this backwards? I'm pretty sure the pump is working because on first start up it was resting against the side of the tank and making all kinds of noise. Would a miswired pump affect the fuel gauge?

I just ran out and checked the wires at the plug in the trunk and they were in fact reversed. Can I just switch them so that gray meets gray and red/yellow meets black? Or will that cause me problems because of the pump wiring?

Good. Sounds like you found the gauge problem. Switch the wires around and your gauge should work again.

But, the tank pump probably wasn't working, or barely working, through the fuel gauge, and at that, running backward. Could be all the noise you heard was the main pump starved for input. This wire reverse happened to me and cost me a tow, when the main pump finally overheated fighting the backward running tank pump.

If the pump is wired so the yellow wire grounds the positive terminal on the motor, you'll need to pull the sender out again, and swap the terminals in the nylon housing. Here's a link to the post where I got help with this when it happened to me: click here
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Art Benstein near Baltimore

Always read stuff that will make you look good if you die in the middle of it.

The gauge works! When you say swap the terminals, do you mean just opening up the plastic sheaths and switching the yellow wire over to the negative and black to positive?

Yes, exactly. Just open up the plastic - it is fiddly, to be careful not to bust off the locking tabs, but that's the idea. Just swap the terminals and coils inside the plastic sheaths. Much easier than doing the whole job over.
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Art Benstein near Baltimore

It may be that your sole purpose in life is simply be kind to others.