1970 JD 400 Industrial

[70jd400]

Hi. I am new here. I just got a new to me JD 400. All in all it seems to be a decent machine. I am having trouble with the fuel gauge. It always says full. I found that the wire going to the tank wasn't there so I fixed that. But the gauge still doesn't change it always says full. How do I know if that gauge not working or if it's the sending unit in the tank?

 

[Phillip w]

Im no help. When fuel gauge quits i use a measuring stick. Welcome to the forum. There is a guy that surfs the forum named txjim. If you can draw him to you situation I sure he can help. He's like a "Mr fix it/mechanical wizard" what ever he says I'd run with it.

 

[Tx Jim]

Welcome to TBN
Thanks for the compliment Phillip w BUT there are also other members of this discussion forum that are as knowledgeable or more knowledgeable than I am about JD tractors & equipment.

For checking gauge with ign switch in on position take sender wire off of sender & touch wire to tractor frame & IIRC gauge needle should move to empty. One can also remove sender(if fuel level permits) & with sender mounting area touching unpainted area of tank manually move float to check gauge operation.

 

[70jd400]

Thanks Tx Jim. I will try that tonight.

 

[70jd400]

Ok so I just got in from moving the wire to a ground spot. I used the light bracket as that is where the light is grounded to. The needle moved to empty when on a ground spot. So I take it that the gauge is ok and the sending unit is probably junk?

 

[jd110]

In my experience, you have about a 95% chance that this test proves the sender is bad. I have had a couple rare occasions that the gauge is still bad even when it cycles from full to empty when grounded out. The only way to know for certain is to have a variable resistor or a known good sender to test the gauge. The reason is because the sender never goes to zero ohms like happens when grounding the wire.