Fuel and Temp Guages

super99

Well-known Member
I asked about the fuel and temp guages not working on my Oliver 1550 a few days ago. I had time to mess with it today. I switched the wires on the temp guage and now it is working OK. I switched wires on the fuel guage with no joy. Then I took the fuel sending unit out of the tank, the wire was disconnected and wouldn't stay hooked onto the unit in the tank, I was finally able to squeeze it enough to stay on and put it back in, nothing. I took it back out and added a ground wire to the sending unit and hooked up the hot wire and moved the float up and down, nothing. I tried using my test light for power from the guage, nothing. I went to the guage, I had power on one side but not the other side. I'm lost, where do I go from here???
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Have you tried grounding the wire that connects to the sending unit?

Ignition on, ground the wire from the gauge. It should swing to full, return to empty when removed from ground. Some react backward, but it should move when the wire is grounded or removed from ground. That test will verify if the gauge is working. If nothing happens, revisit the gauge wiring, possibly a defective gauge.

If it passes that test, look further into the sending unit. Since it is already out of the tank, connect the gauge wire to the terminal, ground the mount ring. manually operate the float, see if the gauge moves. If it stays on empty, there is an open circuit. A bad connection, defective winding or contact inside the sending unit. Having an ohm meter helps, you should be able to read the resistance and see a change as the float is moved. Check each connection on the sending unit with the ohm meter, you should be able to find exactly what is happening, or not happening.

If this is a gas tractor, be very careful, get everything away from the open tank as possible when testing, all it takes is a spark!
 
Often the problems I encountered with non working gauges were 1) A Bad (loose/open/resistive) Ground or 2) The sending unit (basically a variable resistor) was bad or totally open. CHECK THE GROUND FIRST and then the resistance of the sender should vary with its position and never become an open circuit.

John T
 
Does the gauge case have to ground to the instrument panel?? I repainted the instrument panel before installing the guages. I scraped to bare metal where the clamp holds the guage to the panel. Will that work, or do I need to scrape the edges of the hole where the guage goes??
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Its typically the tank itself or somewhere close by that the sending unit gets its ground. The gauge typically has power on one side with the other to the sending unit where its variable resistance to ground determines the needles deflection. Ive seen poor tank grounds cause problems, maybe try grounding the sending unit (jumper wire) at a better location other than the tank ???

I cant say from here if your gauge needs grounded to the dash or elsewhere ??? Maybe just try a good wire from it to a good ground?? I can ONLY say as above how many are typically configured I have no idea on your tractor, sorry..

Maybe the other fine gents here know better how your gauge operates, see what they have to say

John T
 
I don't think the gauge case needs to be grounded unless there is a dash light socket, and then that's only to make the light work.

You can check the case for ground with a test light or volt meter. Ignition on, there should be 0 volts from the gauge case to a known good ground.
 

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