Random F-250 questions

[Brandon Nootenboom]

So my wife and I just got a 2001 F-250 4x4 7.3 6-spd and its got a couple minor issues I wanna fix. I haven't had a chance to check into but figured I'd start here.

First, the fuel gauge stays on full when the truck is on and goes to empty when off. The owner said the fuel tank has been out of the truck before and after it was re-installed It stopped working. If the gauge wasn't hooked back up at the tank would that cause Iit to stay at "full"?

Second, the "door open" light and dome/cargo lights come on when the drivers door is closed and goes off when its open... maybe wires hooked up backwords wherever the sensor is?

I plan on poking around at things later today but wanted to get any insight I could. Thanks!!!

 

[RonD]

Since about 1990 Ford fuel gauges and senders have this setup.
empty/full
16/158 Ohms

So with key on and sender wire disconnected(high ohms) gauge would go to FULL
With key on and sender wire Grounded(0 ohms) gauge would go to EMPTY
With key off there is no power to "see" the ohms, so gauge would go to empty via the spring.

So yes disconnected sender wire would show FULL, or an ungrounded sender unit would as well since that would still be a "disconnection".
Generally there are 4 wires to the fuel tank;
Fuel pump Power
Fuel pump Ground

Sender wire to Gauge
Sender wire Ground


Dome lights have power to them all the time, so not on the key switch, if you test the dome light it should have 12v all the time but no ground(all doors closed).

These lights are turned on by grounding them, so door switches are grounds not power.
It could be the switch is broken so is grounding when door is closed then loosing the ground when opened.

 

[adsm08]

Ron has most of it right. I think he missed one important point in the fuel gauge. The 7.3 diesel only has 2 wires into the tank. There is no in-tank pump, just the lift pump on the frame.

 

[RonD]

Oops, thanks for the correction ..........again lol.

 

[adsm08]

Everything you said would be right if we were working on a gasser. Also, you aren't the only one who thinks that the diesels have an in-tank pump. I just had an argument with a guy from one of the shops that buys parts from us about this on Friday. He insists he has replaced them before, even though Ford, NAPA, and Auto Part International don't list anything but the lift pump.