87 Bronco II Fuel Gauge not working correctly ?

[raggedyann]

I replaced unit in tank last yr. my fuel gauge shows 3/4 full and only has a couple gallon in tank. bad ground or float ??

 

[cammeddrz]

there is a yellow wire that runs all the way from the sender, to the instrument cluster.

grab your multi-meter, set it to ohms, touch one side to ground, and the other to the yellow wire. it should read 16ohms empty, and 158ohms full. with an even spread between them, (i.e. 87ohms for 1/2 tank, 51.5ohms for 1/4 tank etc.)

go put a few gallons in the tank, and see if it changes, if it changes, and the gauge doesn't, you have a bad gauge, if it doesn't change, the sender is bad, either the potentiometer inside it, or a float issue

 

[raggedyann]

Thank you, I will do this in a day or so.
question ? can I access the yellow wire this side of the tank or be able to get to it without dropping the tank ? and I leave yellow wire connected while testing , right ?

 

[cammeddrz]

The harness, runs along the frame. You can access the wire anywhere. It has a big connector under the hood on the driver side, at the firewall.