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4430 JD Fuel Sending Unit

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Baileyja

New User
I recently switched my 1974 4430 from a 24 volt system to a 12 volt. My fuel gauge started showing full or over full all the time. How is an easy way to tell if it is the sending unit? Is there a different one for a 12 volt system? I checked it with ohm meter and it doesn't show much difference in readings whether open or closed. Thanks.
 
Trying to figure out what's going on here, it's to early for April Fool's???

They (US versions, anyhow) left the factory with two six Volt batteries in series making a 12 Volt system.
 
Well, it was 12 Volts (-) ground before, and you must have connected the new battery (-) ground as well, or you would have let the smoke out of the alternator.

ASSUMING the charging system works, ground polarity is correct, so nothing should be any different from the fuel gauge's point of view.

STRANGE that it started reading funky at the same time.
 
I know that is right. Might just be a coincidence.
It is negative ground now as it was when I had 2 batteries. Positive on battery 1 to starter, negative of battery 1 to positive of battery 2 and ground to negative on battery 2. What should the ohms reading be if the sending unit is good?
 

"What should the ohms reading be if the sending unit is good?"

I don't have my shop manual at hand, and I don't want to toss a potentially wrong resistance number out from memory, but you can try this...

Take the wire from the gauge off of the sender and ground it to a good, clean chassis ground, and turn the key switch "ON", the gauge should move to "FULL", then drop to "EMPTY" when the wire for the sender is ungrounded.

If it does that, the gauge and wiring are good, trouble has to be the sender.

Also, note the the sender needs to be grounded, as I recall, this wouldn't have a separate ground, but would be grounded by it's mounting screws to the tank, which is mounted (and hopefully grounded) to the chassis.
 
I had a different issue but wanted to share the fix. The gauge was reading empty. Found the wire from the sending unit to the firewall had chafed through close to the radiator and was grounding out. Thanks for the advice.
 
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