1984 f250 4x4 auto was 351w, 460 swap about 20 years ago. Dual metal tanks. Front tank currently not in truck.
Replaced selector valve on frame rail and new sending unit in new rear tank. Old valve and sending unit still work but rusted pretty bad.
My fuel gauge will not work unless I ground the sending unit. I have old sending unit,(tested fine on ohm meter) just plugged into either two prong tank plug. Thought maybe my new rear sending unit was bad. But gauge readings seem very accurate on front or rear with old float sending unit plugged in and grounded.
If not sending unit not grounded gauge reads empty. Checked all grounds that I know of,taillight,under dash pad.
Even reinstalled the old selector valve to eliminate something in new one. I need help. Wiring diagram may help also.
Thank you,Craig

 

Gary Lewis has the 1981 & 1986 EVTM's on his GarysGaragemahal website.

I'm not sure how (or if) your '84 fuel sender wiring would differ from either of these years, but Ford was pretty good about keeping the wire colors consistent.

 

Electric or Mechanical Fuel Pump?

Built in Tachometer?

 

The only difference is that in '86 Ford did away with the hash and dot marks, going with stripes. So an '84 using the 1986 EVTM would have the same colors just stripes instead of hash or dots.

 

The sending unit is supposed to be grounded, that is how it works. It should have a screw with a ring connector connected to a ground wire in the harness.

The sending unit's resistor varies the ground to the gauge, the guage is fed power all the time from the cluster.

If you can't resolve the ground in the harness, just run a new ground wire over to a good place on the frame, or run it up front to somewhere under the hood out of the weather.

 

Thank you all for the advice ,I figured out yesterday it was a ground issue. Turns out I had a bad section of wire about mid frame although the wire looked perfectly fine. I also found an intermittent break coming from rear sending unit wire about a foot into main harness. Btw my 84 still has some wires with hash marks,but also striped wires too. Only took me about 5 hours over three days to figure it all out. Electrical is not my strong point ,lol

 

Thanks for the update as it may help others.

It always takes time when chasing an issue like this to find why, you did good.
Dave - - - -

 

Glad you found it. Congrats!

And, the hash and dots continued through '85, but changed to stripes in '86.