I have a 83 Ford 1 ton van, it has 2 fuel tanks, when I purchased it and filled both tanks the foward tank read a little more than half a tank, the back tank read empty, after taking the van on a road trip and running the back tank out of gas (because I was going to drop the tank and pull out the sening unit) I went through and cleaned all the contacts including the grounds and found a very dirty and loose ground on the back tank. Thinking this might fix the problem on the back tank, I ran to the gas station and put in 8 gallons in the back tank thinking this might have fixed the problem but still the same problem. I have measured the resistance of the sensing units of both tanks with a VOM. The front tank which I think is now about half full reads about 40 ohms but shows alittle more than 1/4 tank, the back tank with 8 gallons in it reads about 60 ohms but still reads empty. The voltage to the the sensing unit on the VOM seems to be a pulsing from 1 volt to 5 volts a about 1 cylce per second (Hz) and I am not sure if that is normal. also I seem to have normal indications on all other dash gages. I have read every post on here and have not found the answers I need.
1. what is the resistance range of the fuel level sensing unit (full and empty).
2. does the voltage to the sensing unit pulsate (if so what are the values.

 

I also have 3 wires going to the fuel sending units
1 is the ground
2 is the pulsing 1-5 volts at 1 Hz
3 I dont know what it does.(could this be a power wire for a fuel tank fuel pump, but it does not seem to have 12 volts).
I have not been able to find a schematic.
Please help me.

 

went to Napa and picked up a new IVR, after spending all day trying to get the instrument cluster removed, (by the way how do you get the speedometer cable disconnected?) installed the new IVR and turned it on, and guess what, both tanks read empty. I measured the voltage to the fuel tank sensor and it was pulsing but much different then the orginal. it would go to about 10 volts but only for a fraction of a secondthen it would go to zero volts for about 3 seconds, so at that point I decided to open my orginal IVR and see what made it click, quite simple, it is a spring loaded switch with a coil of wire wraped around it, when the contacts are closed the coil gets hot and the spring will open the contacts removing the voltage, kind of like a flasher.
any way I cleaned the contacts which were dirty and then re-adjusted the spring tension and son of a gun it worked, I just finished calibrating it and seem to be working fine, just wish it was easier to get to the back of the instrument cluster.
thanks
bill
P.S. still dont know what the third wire is going to the fuel sensing unit.