Full and oil gauge work on and off I think its bad grounds where would the ground wires be

There might be but it is unlikely a fuel gauge is fused alone; usually if it is a fuse other things will stop working too but I suggest you are guided in this matter by your car handbook.

Problem is probably wiring and in particular the grounding of the fuel tank sender unit. It could be a faulty sender but they are usually quite reliable.

Test by disconnecting the wire from the sender unit at the fuel tank and short to a good ground and the gauge should read full. If the gauge wire is in a block with other wires it will be necessary to positively identify the gauge wire before testing.
If the gauge reads refit the wire and duplicate the ground wire to a known good ground. If the gauge still reads the fault is a bad ground to the tank sender unit and if it doesn't the sender unit itself is probably faulty.

If grounding the gauge wire does not produce a reading the fault is the wiring to the tank, the supply to the gauge or a problem with the gauge itself.

Check for a frayed wire touching metal and grounding out. The gauge works on resistance and it registering full indicates a short to ground. Either that or your gauge itself is bad.

well its not connected>? or you forgot to ground the ground wire?
if you had a DMM meter , this would be easy,
you can measure the sensor ohms, at any time with tank in car.
and id have never put back any tank with out checking it first.
not me, pulling tanks is no fun.
and empty tank the gauge sender is at max ohms, (lever down)
so is about 100 ohms and 10 ohms full (ball park) RTM
read the FSM read alldata.com
heck the FSM has a flow chart for these tests. amazing huh?
i dont use it, i use my meter and ohms law.
ill now look online at alldata.
the only think complex is which of 2 systems it is,
in the late 90s most cars changed. to indirect way.
ok , i looked, your car is direct way, (cave man)
its just 2 parts, a gauge and a sender. (sure wires)
the sender is grounded at G751
if the dash temp guage works , then the fuse is not blown , fuse 1.

the tests are cave man simple , all FSM show this.

1: unplug the Yellow/Blue sender wire, at any point
from front (gauge) to sender, any place, there are many.(4 junctions)
now, on the upstream side, key on, and ground this pin for 1min
max, if guage moves pull the ground. (i use $#194 lamp for tests )
i connect my lamp to ground and the other side to the guage,wire.
then key on and see guage move. bingo gauge is 100% good.
cave man easy. (

now the sender.
i measure the ohm.
DMM on 200 ohm scale if manual meter.
i connect black meter to body ground (shiny steel not plastic)
i connect red lead to down stream wire above..Yellow/Blue
it must read 100 ohms empty
not 0 ohms.
not infinity.
if read infinity? the wire is cut, or gound it open or the sender is bad.
if reads 0, the wire is grounded to the body or the the sender is bad (shorted)
do not take my facts on ohms as verbatim,
read the FSM and get the facts.

but i think your tank sender wire is shorted to ground.
some gauges work backwards, and my poor online version
dont cover this. well.
unplug the sensor does guage go full or empty?
most go empty, but not all.
use the lamp to test the gage, get to swing both ways
with lamp to ground and with lamp and wire disconnected.
cheers.

Yes, the sending unit is in the tank. If you unplug the connector at the tank and ground the gauge's sender unit wire to metal, with key on, the dash gauge should jump to full or near full. This verifies the dash gauge is working properly, and the problem is with the sender unit in the tank. If the gauge doesn't move when grounded, then the gauge or wiring from tank to gauge is not correct.
Good luck.

Likely, it's the sender unit in the tank. To check wiring and your dash gauge, you can pull apart the connector at the fuel tank, find the wire for the gauge sender unit (its color coded-I dont kinow what the one for your car would be), and on the harness side(the one going to front of vehicle) use a jumper wire and ground that wire to the car frame(get me? you want to ground the wire going to your dash gauge)-with key on, your gauge working properly will move up to half-way or even full. That tells you your dash gauge is working and your wiring to gauge is good. If gauge doesn't move when grounded(double check for a good ground), then your dash gauge may be bad.

84 ford ranger gauge not working ./ tom 591-570- 3663

Its either a bad ground wire to the sending unit. The sending unit itself. The gauge itself.
If you ground the wire that connects to the sending unit in the tank the gauge should show full. Disconnected the gauge should show empty. this will test the gauge. Most often there is a ground wire going to the sending unit which corrodes.
Lee

According to what I read, test the gauge first. Hook power to where the white wire attaches. Hook a ground to the black wire connector. The gauge should rise to full. (May take a while). When on full, the tan wire connector to same ground. It should go to empty. If both work, gauge is good. To test sender, in the empty position, your ohm meter should read 0-2. 1/2 tank should read about 40, and full should read 84-88 ohms.

Jess, Make sure you don't have the ground and sender level circuits crossed at the gauge. If the needle is pegs to full it indicates an open circuit, if the needle pegs to empty it is indicating a short to ground.
Let me know.
Regards,

hello this sounds like a bad ground to the gauge cluster first thing to try with the key in the on position tap at gauge area see is there any change if not open dash area were gauges are wiggle to see if they are grounded good into dash grab a test light take end put to the ground on one off the gauges touch other power wire with probe while key is in the on position same for both gauges if no difference reinstall you need to check grounds on both gauges by tracing wires it might be easier if you locate your oil sending unit take the wire off attach alligator clip to wire now touch positive side of batterey if it lights grounds okay trace back to units oilsender,sending unit at gas tank goodluck please rate