I have a 2001 duramax with a xtra fuel tank in the bed/ tool box. The tank has no fuel sending unit and I would like to add one to read off of the exsisting gauge. I ordered a unit from j.c. whitney and made all connections. My problem is the gauge reads 3/4 full when full and 1/4 full when empty. Does anyone know of a supplier of after market sending units that will work with the durmax?
I called transfer systems and got no where. I was told they do not sell just the sending unit. Any ideas. The tank is around 30 gal and the height is 6". Thanks...

Don't know which unit you got but the float must be able to travel the entire height of the tank. If it was the universal sending unit it has to be cut to fit. The best way to calibrate it is to move the float with the sending unit connected to the guage the distance of the full and empty positions and be sure the guage is indicating correctly at those two positions. Make your adjustments to get the correct indication at the full and empty position. It usually requires bending the float arm. Some may have a screw to adjust the float travel. It is all in the travel of the float from full to empty.

Caution don't run the tank down to empty. Know where the real empty position is. Getting air in the system is no fun. I speak from experience, twice.

Tom

I would check the sending unit you have to make sure it is capable of reading across the range from E to F. To do this, remove the sending unit from your tank but leave the wires connected. Manually position the float arm to the full position and check your gauge, repeat at the empty position. If it's reading in the right direction, which your post indicates it is (more fuel = a higher reading on your gauge, less fuel = a lower reading), I believe the sending unit should work with adjustments as described by Tom. However, wIth a tank depth of 6", I would expect you'd have to make some significant adjustments to get accurate readings - perhaps even having to shorten the rod that holds the float. If the sending unit itself is incapable of changing resistance to the degree necessary to have your gauge read completely full or empty, then you can either continue using it knowning that, or obtain a new sending unit. I got mine from American Tank (http://www.auxtank.com/auxtank/home.asp) in Texas and it works very well (cost about $45 or so, IIRC). It also required adjustment by moving the pivot point (the potentiometer) up or down the rails and by bending the arm that holds the float. American Tank will ask you how deep your tank is and will build the sender accordingly so as to require minimal adjustment upon installation.

Good Luck!

Don

I did remove the sending unit and swing the arm from full to empty. I then took an ohm meter and measured the resistance of the unit I have. it read 87 ohms.

I then took a resistor starting at 100 ohms and worked my way up placing it between the gauge wire and ground, and found that the gauge had full movement when it was open ( gauge reads full) and a 200 ohm resistor hooked to ground the gauge would read empty. The low fuel light came on.
So by adding a 100 ohm resistor to the present unit I now get a deflection from 1/2 tank to empty. this helps let you know that when the tank is getting neer empty to switch to the other tank.
I would like this aux tank to work like the other. I will give American tank a call and see if they can help me out. Thanks for all the help......