how do I bench test a new fuel gauge ?

I use a variable power supply at around 1 volt or less, and ¼ amp or so to check them. You could use an AAA battery for power and a cheap potentiometer on the negative side.

Did you get the different resistors to try yet ?. You will need those or a variable resistor.

As far as bench checking. The fuel level gauge should not draw hardly anything for amperage so you could get a basic 12V 10A max output power supply.

On the power supply you will have two terminals (12V+ and Ground).

One terminal of the gauge should go to the 12V+ while another terminal on the gauge to ground, and the third terminal on the gauge to the sending unit. You will also have to have a jumper wire from the mounting ring of the sending unit tied to the ground on either the gauge or the power supply.
You must also get the proper terminals on the gauges connected to the correct terminals on the power supply and cannot have them hooked up incorrectly.

I know you have been having problems with your fuel level system and maybe take it to a better stereo shop that does service work and ask if they can bench check it for you (but you will need to identify which terminal goes to what on the gauge and sending unit). Sometimes a fresh head can see the problem you are having and get it corrected. I too sometimes look at things and the problem is right in front of me but sometimes asking another co-worker whats up and he might see it right away and then it clicks in my head.

I wonder too if you don't have a power or ground problem feeding the gauge or maybe some bad jumper cables. I just had a cheap set today give me screwy readings while wiring up some power seats for a street rod and found out the wire that was crimped under the rubber covered alligator clips were loose so I got some thicker wire (16 gauge) and reused the alligator clip ends but then soldered the wire to the clips and they are much better and more reliable now.

Jim

I orderd a 0-100 ohm resister for testing. Why do you need to ground the mounting ring? It is not grounded in the plastic dash piece. I want to get this figured out as I will be set to check some other gauges.
Thanks !!!

Slow down. What I said was "You will also have to have a jumper wire from the mounting ring of the SENDING UNIT tied to the ground on either the gauge or the power supply."

To complete a circuit you need the return path. With one wire going to the sending unit you need the return ground path back to the gauge or the vehicles ground.

Jim

Okay guys, just got back to checking the group. I wound up doing the bench test as mentioned above. Kept getting wierd readings and finally ohmed my test leads and found a bad lead, I re-did it by soldering the ends. Now they are good but still not getting the proper readings with sending unit (in drivers seat) and new gauge. Driving me nuts, found this site on the net and ordered their fix http://www.fix-a-gauge.com/ . Looks like some sort of in line resister-- when I ohm'd it I read 88 ohms. I pulled the new gauge out of the dash and put this device on the back of the gauge, ran my test leads to the sending unit laying on the seat and Viola--- it now has the correct reading!!!! I never could get the other new gauge to work, no matter what I did so I sent it back to NPD for refund. I then filled the tank up with gas and rehooked everything that I had unhooked. Turned the key and Now read full tank of gas!!
Thanks for all the help guys !!!
Hair growing back in----