Hi i just bought an 85 f250.lifted with a 351w.but the gas gauge dont work and i was wondering if anyone could tell me how to wire one in it.or maybe have a diagram or pics on how to.thanks

 

Does the oil and temp gauge work? If they are working then the problem is most likely elsewhere like the tank sender.

I have some diagrams here:
http://75.95.181.105:86/F150/Dual_Tank_Selector.html

 

Interesting, my fuel gauge won't work and neither will my temp. What are you suggesting that it could be, in the wiring behind the dash?

 

Have someone watch the gas gauge while you ground the wire that goes to the sending unit in the tank, which you can just pull off the stud of the sending unit. With the key on and that wire grounded the gauge should go to Full, although it takes a few seconds.

If that doesn't work the problem is in the wiring. If it does work the problem is with the sending unit. The bolts holding the tank in are usually long enough you can lower the tank and get the sending unit out w/o taking the tank out all the way.

Does the oil pressure gauge work?

 

The fuel, coolant temp, and oil gauge are all powered by a voltage regulator in the instrument panel. It pulses 5 volts DC. If all 3 gauges don't work then the problem is likely with the VR or wiring to it.
If one or more of those work then I would look at the senders(s).

 

My Ford shop manual says to not ground out the senders as a diagnostic. Instead they suggest to use a resistor (10 ohms = full tank & 73 ohms = empty). Another way to test is to measure the voltage at the sender connecter. It should pulse 5VDC about every half a second.

 

Bingo. Which is why I asked about the oil pressure gauge. You told us that the temp gauge doesn't work, along with the fuel, but didn't say about the oil pressure.

 

That is what the manual says, but few of us have those resistors available. And, while it may be possible to cause some damage if the wire were grounded for hours, since the current is turned into heat that actually moves the gauge it should not be a problem if done for short periods. Many of us have done it with no problems.

Having said that, my lawyer son would urge me to also say "but I am not accepting responsibility for any damages that might ensue". Again, what you are saying is accurate. But, the quick and dirty grounding test has also worked for years.

On the other hand, checking the voltage at the connector is something I hadn't thought of, and it is a one-man operation. Duh! So, I vote for that test. If you have the roughly 5 volts you'll know that both the voltage regulator and the wiring are good, so the problem must be the sender, which is frequently where the problem is since it sits in gasoline all day long.

 

They may be worried about damage to the gauge if it is allowed to 'peg' hard for a long time? Should be OK if the grounding is removed as soon as the pointer starts to swing.... you will know it is working at that point.

 

All my guages but the fuel guage work.so it might be the sender?.ill try grounding it out in a bit freakin raining hardcore rite now.

 

I'm betting it is the sender. They are notorious for going bad. I've owned several of these trucks and less than 1/2 of the senders have worked properly.