MF 35 gas gauge

garymck · Jul 8, 2015

The gas gauge stopped working so I ordered a new one. When I hooked it up as directed, the gauge reads backwards. When full, the tank shows empty.I took the sender out of the tank and the gauge works OK but backwards. So I hooked up an older sending unit. Same thing. I tried to hook up another ground. No change! I even tried another spare gas gauge. Same thing. Backwards. I'm stymied. I tried so many things. I think I even switched the wires on the gas gauge in desperation. Nothing.

Inno · Jul 8, 2015

I would think that switching the wires should work. No, on second thought that would make the gauge deflect backwards which is not what you want.
All it's doing is varying the resistance between ground and the neg terminal on the gauge to give you a proper reading.
Essentially 12V across the terminals with the correct polarity will make the gauge deflect and read full.
I'm wondering if your sending units are designed for pos. ground and the tractor is neg. ground or something like that.

garymck · Jul 9, 2015

1) I hooked up a generic gas gauge to a spare MF sender (outside the tank). Works fine.
2) I hooked up a generic gas gauge to the sender in the tank, works fine.
3) I hooked up the replacement gas gauge to the removed spare sender, reverse reading.
4) I hooked up the replacement gas gauge to the sender in the tank, reverse reading.

I hooked up the wires in the back of the replacement gas gauge as indicated in the instructions. I think there must be a demon in the instrument cluster.

Hay hay hay · Jul 9, 2015

Not to be a smart aleck, but that is why i use a stick. Easier and faster and maybe more reliable.

Inno · Jul 9, 2015

Is your 35 neg. ground or pos. ground?

garymck · Jul 9, 2015

It is negative ground.

Inno · Jul 9, 2015

Sounds like it's the gauge......for some reason can't put my finger on it. It's a simple circuit to be sure. Is it possible the replacement gauge was labeled wrong? Could it have been designed to go in upside down and they printed the E and F the wrong way........that's the only thing that seems to make any sense to me at all.
Something is really bugging me about this. So with no power applied to the gauge at all the needle reads E? When you connect power and the wire from the sending unit with an empty tank it reads F?
Could you post a picture of the gauge? When the sending unit float reaches the top of the tank the resistance between it and ground should be at or close to 0 ohms. When the float reaches the bottom of the tank it should be much higher than that, not sure what the resistance range of the sending unit is.

garymck · Jul 9, 2015

Well, I fried the replacement gauge. I was experimenting with the unit. What I didn't like about it was that the terminals in the back were under the bracket used to snug up the unit to the dash. I think that when I put back the power, a wire shorted on the bracket and there were some sparks and a burning odor. End of unit. I put in the generic gauge where the bracket does not interfere with the terminals. The gauge reads full on a full tank. When I get over my frustation, probably tomorrow, I will partially empty the gas tank to see if the gauge registers a change. If this doesn't work, I will either have to get another MF gauge or put up with what I have. Thanks for your comments.

garymck · Jul 10, 2015

Well. The generic gauge works with the MF sender. How accurate? I don't know but at least it is moving.

Inno · Jul 10, 2015

Well, I guess it is better than no gauge at all. Both my tractors are gas so if it runs low or runs out it's not a big deal. If they were diesel I'd want to make sure I had a good gauge in there.

MF 35 gas gauge

garymck

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Inno

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Hay hay hay

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