How can i fix the gas gauge on my 1988 dakota with the 3.9l?

Could be a number of things.
The fuel sender could be at fault not sending any voltage to the gauge. One way to check this would be to find the signal cable under the rear passenger seat, short them together and see if the gauge moves.
If not that then the gauge could be borked

check for a common fuse( Instrument panel)

Mine does something similar. Dad said that it could be the gauge could be busted. I would take it in to get it looked at. Sorry

WHEN EVER YOU WATER IN THE OIL IT'S NOT GOOD TWO POSSIBLE REASONS BAD HEAD GASKET OR BAD CYLINDER HEADS

idle control valve its about 50.00 to 75.00 I had same problem

you need to replace the sending unit inside the gas tank, if you have a broken gauge then replace the gauge, most of the time is a sending unit in the tank that goes bad, drop fuel tank to replace. heres a picture of it, hope this helps.

mcdevito75 here, A Faulty fuel pump could be the cause, Or and a dirty gas filter, have the shop check it out.

find the actual gauge sender in the gas tank, ground the wire to the tank and see if the gauge moves(ignition on)

If the gauge moves, replace the sender

need to replace the sending unit

If its just your fuel gauge that has stopped its not a fuse... the fuel sending unit's fuse is not dedicated to just the sending unit.. Sounds like sending unit failure.