i bought a 77 ford f100 and the guy i got it from put a tank behind the seat.the one underneath is rusted.the sending unit in the tank behind the seat was way rusted! how do i know what year sending unit to put in it?since i dont know what year the tank is?i bought one off e bay that looke exactly like the old one but cant get the fuel guage to move!!! i grounded it to the cab.my amp is grounded to the cab and it works fine? i jumped the sending unit to the groun and the needle goes all the way up! does that mean the sending unit is wrong????? help!!!!!

 

test light hooked to the p[ower of sending unit blinks.test light to the fuel guage wire by itself blinks too

 

You have to make sure the ohm rating for the sending unit matches your gauge. I believe our years are 75-10 ohms.

 

Yep, you should remove the sending unit and measure the rheostat resistance with the float arm all the way up, and all the way down.

 

so check the ohms on sending unit make sure it matches the ohms called for the year 77?

 

With the float arm all the way down, the resistance should be close to 70 ohms. With the float arm all the way up, the resistance should be close to 10 ohms. That's all.

 

thanks i will find a ohm tester and see what mine reads.thanks for the advicehopefully ill be rockin soon!

 

What you did in posts 1 and 2 indicates sending unit problem.

 

did ford make a behind the seat tank for the 77.if not what year will work if i need 70-10 ohms?

 

I'm going to guess and say any 67-75 in cab tank sending unit will work.

 

thanks ill check it out

 

Have you actually measured yours yet? It may already be the correct sending unit in the first place.

10/70 ohm is a VERY common resistance range for Fords. That's because most of the gauge windings are all the same. You're not going about this properly. Stop focusing so much on what is used where and simply get out your multimeter and measure what you have. You've been posting your question in one form or another for the last week and it could have been solved long ago.

 

all the way down it reads 7 up 0
need a new unit

 

Hold the phone. What does the fuel gauge read when the sending unit is hooked up like normal?

 

the fuel guage reads empty never moves unless i jump the ground to the power wire on sending unit, then the needle goes all the way up!