Removing the rear tank.
 

We had a truck come through our shop that we had to give up on. 2000 K3500 cab and chassis with a 5.7. Previous owner had removed the rear tank but installed a tank on the welding deck. The fuel gauge didn't work properly but it did move. Current owner wants to use the tank for diesel fuel for his welder. We removed the transfer pump, disconnected the sender for the second tank and replaced the fuel tank module in the main tank because the gauge circuit was open. We could not get the gauge to only read the front tank for love or money. What signal does the VCM need to see to work? We have tested all the wires with a halogen bulb to rule out bad connections. The gauge responds correctly to the scan tool. Help?!

Re: Removing the rear tank.
 

Not sure about the newer stuff, but the older gauges work off resistance (ohms). I have never seen a factory GMT400 or 800 that had a rear tank, just the one side tank unless someone added one on top of the flatbed.

Re: Removing the rear tank.
 

There is a balance module mounted along the left frame rail. It takes input from fuel level of each tank and sends fuel level to the gauge. It also controls the transfer pump that pumps fuel from the rear tank to the main tank.

That balance module needs removed. The wring for the fuel level for the front tank needs hooked up to the wiring before the balance module.

I did this on my c3500hd rollback. I had to remove the rear tank to make room for hydraulics. I’ll post some wire diagrams within a few days.

Re: Removing the rear tank.
 

It was an option only on cab and chassis trucks.

Re: Removing the rear tank.
 

Here is an older thread that I posted diagrams in:

http://67-72chevytrucks.com/vboard/s...d.php?t=674993

Re: Removing the rear tank.
 

Thanks, learn new stuff every day on these vehicles of ours.

Re: Removing the rear tank.
 

This looks helpful. Of course, I don't have the truck to try this on but I'll see if the guys can get it back while I'm off recovering from carpal tunnel surgery. At least I have time to study the diagrams.