4020 gas, Pos gnd, fuel gauge problem

I have a 1966 4020 gas with 12 V Pos. ground, single battery. I believe fuel gauge is bad. There are 2 connections on the gauge.

I confirmed the one connection is power and it has power (test light lights when I ground it). I shined up the connection on the gauge and it fits tight so I believe it is getting power.

I was expecting when I grounded the other post (sending unit connection - orange wire) that it would peg the fuel gauge, but it moves only about 1/8" up on the gauge (same as it does with sending unit) when I turn on key. I was grounding direct to the pos gnd of the battery when doing so.

Is this a valid test?

The sending unit has one wire and when it is connected to the gauge and I turn the key on, it moves the needle up by only 1/8" or so and the tank is almost full.

thanks in advance
bruce harle
De Soto, WI

This post was edited by bruceharle on 05/30/2023 at 07:43 pm.

Im NOT a New Gen person, however on older units if you direct connect a gauge itself
to power it should full peg AND IF SO THE GAUGE ITSELF IS OKAY. If the sending unit is
okay and the gauge cant properly register all full to total empty, EITHER the gauge is
bad (or incorrect resistance range) orrrrrrrrrrr so often THERES A WEAK RESIITVE
GROUND RETURN PATH but where ?? I cant say. Often rust or a poor physical connection
is at fault

John T

Update:

I confirmed the gauge was bad as per your recommendations - thank you!

Thought I would spend the additional money and purchase replacement from JD dealer to minimize problems and headaches. $200 and not good result. Had a light in it and was much thicker than OEM gauge which would be hard, if not impossible to install. Returned.

Thought I would order the one from here on YT tractors, assuming they would have a better one that would likely fit as these old tractors is what this site is all about. Strike 2, it was similar to the JD dealer, but without light. Also, no directions and not clear at all which post is gnd (pos) and which is the sending unit. I was afraid I would burn it out guessing, plus being thicker it was going to be a pain to modify the retainer to make it work. Hopefully they let me return it. If able, I will attach pictures.

Today I looked at Steiner tractor parts and they actually had dimensions of their gauge. Measures to the same thickness, so I am hopeful it will be a swap replacement. We shall see in 1-1/2 weeks. Also in the picture of the part it showed which connections were for which wire. cautiously optimistic.....

thought I would post to help someone eliminate the trial and error I encountered.

couldn't figure out how to attach a .jpg picture to this...

bruce
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