update on 4020 fuel gauge

have power to gauge. When u ground gauge it goes all way to full. Does the same with or with out the sender attached. I know its not the sender its brand new and I know its the correct gauge and sender. Tried two diff new senders just to be sure. Have tried everything I know and dune everythihng suggested to me already still with the same result 160dollars in new parts and still no working fuel gauge

1.) Are you grounding the sender wire AT THE TANK to get it to read "full" proving the gauge and wire up to the sender are good??

2.) Are the tank and sender grounded? Try running a temporary wire from one of the sender mounting screws to a GOOD chassis ground.

I know the wire to the sender is good I replaced it to b sure. It doesnt seem to matter weather the sender wire is attached or not as soon as I ground the gauge it goes to full. And I did the wire from the sender to the frame to ground it still with no diff Im really starting to think I have a short or other elec problem and considering just buying a new harness

I am proud of you for sticking with it! Listen to Bob below. You are giving us some good information. Here are a few more questions: 1) When the wire is UNHOOKED at the TANK it should read EMPTY. Does it? If it should read full when unhooked at the sender and empty when unhooked at the gauge, then the wire itself is grounded. 2) If and only if you have passed test 1 above try this: Run a known good wire(one that has continuity) from a spot that you have shined on the base of the sending unit(not the tank itself) back to a shiny spot BETWEEN the two batteries and it should work. This eliminates a possible bad ground between the BASE of the sending unit and the TANK. It also eliminates a possible bad ground between the TANK and the middle of the batteries. A person could also 1) Drain the tank and take the sender out. 2) Run a known good wire from the gauge to the sender. 3) Run another known good wire from the base of the sender back to the center of the two batteries. 3) Turn the switch on and now you can manually move the float on the sending unit up and down and the gauge as well should go up and down. 4) Let us know what happens!

If I unhook it from the sender it reads full and Im pretty sure it does the same if i unhook it from the gauge. Iv tried so many different things its all startin to run together.But that wire is new I just replaced it. I did run a wire from the sender to a spot on the frame i shined up that my deere mechanic suggested to do with no result. Im gettin really frustrated all this to get a gauge workin.Ive checked my power wire and have -12 volts ive checked for resistance in the sender.All the tests I try everything is what its suppose to be and im left scratchn my head.

You DON'T need a new wiring harness, if you've run a new wire from the gauge to the sender.

The one thing we need to know here you are NOT being clear about.

EXACTLY what do you mean by "as soon as I ground the gauge it goes to full".

WHAT are you grounding... the terminal/wire at the SENDER, the housing of the gauge itself, or the "ground" terminal on the gauge itself (if it has one)?

There is a simple test for fuel GAUGES... with a certain Ohms resistance value to ground through the sender, it will read "full", and with a certain resistance value to ground, it will read "empty".

If we knew that value (anybody got a factory service manual handy) you could use one or two discrete resistors and verify the GAUGE is OK.

Likewise, there should be resistance "spec's" for the sender when "FULL" and "EMPTY", which would be easy to verify with an Ohmmeter.

BEFORE throwing any more money at this, AGAIN verify the gauge and sender match and get the "FULL" and "EMPTY" resistance values for the sender.

HOPEFULLY, the service manager at the dealer you have been shoveling money to can look up those resistance values for you.

I'm GUESSING your gauge wants to see either 30 or 90 Ohms through the sender to ground for "EMPTY" and close to zero Ohms through the sender for "FULL", depending on the setup used.

On some systems, a ground through the sender will make the gauge read full, some are set up exactly the opposite, a ground through the sender will cause an "empty" reading.

Deere has used BOTH systems at one time or another, also, there is a possibility of a (+) or (-) ground system with a gauge to match.

If you happen to have access to a "resistance decade box" (a piece of electronic test gear) it would be an EASY matter to see what resistance values at the sender are required to make the gauge read full and empty, but the resistance value is the same, just the action of the float for a given resistance is the opposite.

There's a link below to s site about CAR gas gauges. The Deere system is likely very similar to one of the GM systems.
A little more information...

The gauge must NOT read the same wih the wire hooked and unhooked. The gauge itself must be grounded to the center of the batteries. Is it? The part number of your positive ground gauge must be 54427. Is it? As Bob said, a new harness is just money thrown away. The sending unit should have approximately 240 ohms in one direction and around o ohms the other. What do you have? Stay with it! I will email you after while.

I know they can be fusterating, sometimes I pull the sender and then put the sender to gauge wire back on and atach a ground wire to the sender mounting flange and lift and lower the sender arm and watch the gauge for action, I'm still thinking a ground problem or wrong sender unit.

Hello, I have a 1967 John Deere 4020. About a month ago, I decided that I would fix the fuel gauge on it. I bought a new sensor from AI Products and I bought a new gauge from them also. When I installed them, the gauge would show about 3/4 full whether it was empty or full. I played with it for about 3 days, filling the tank and draining it, and moving the gauge up and down outside the tank. Nothing seemed to work or help, so I went to John Deere and bought a new gauge and sensor from them. When I installed them, I had the same problems. I took the sensor back and they gave me a new sensor. After all of this, I have still not been able to get this to work. I now have 2 gauges and 3 sensors and still cannot get an accurate reading. I just thought you might like to know that you are not the only one who has had problems with the sensor. Regards, Bob

I guess it can't hurt to post my 1964 John Deere 4020 fuel gauge dilemma one more time. Sent original stock gauge to Jerry Trcka (he advertises in Green Magazine) for repair and refacing. Put gauge back in...did not work. Called Jerry and he suggested getting new sending unit. I got one from local Deere dearler. Put it in but gauge still did not work. Called Jerry and he agreed to check gauge again. sent gauge to Jerry (second time). Checked out fine. Put gauge back in but still can't get it to work. I see no reason to get a newer style gauge if there is nothing wrong with the original. I guess I have the correct snding unit since it came from Deere. I would ask that any mechanics on this site respond as to whether there are different sending units for different model tractors. If so, which model (part number) is correct for 1964 with original gauge. Thanks!