Help needed please - sending unit 1955 F250

OK, I here is the hair pulling question:

Tank is new -- Sending unit is new for 6V or 12V -- Stock 6V gauge
Tested all at my desk and worked.
Placed gauge, sending unit and battery back into truck.
Tank is 1/2 full and float in positioned to the right (back of truck)
turned on key and fuel gauge went to full.
Took fuel gauge out and ground off -- still went to full on gauge.

I guess what I am asking is -- can I be grounded out on my tank somehow or do I just have the sending unit not hooked up right or grounded or ???

Let me know anything cause I am running out of hair! Thanks...Chris

 

Does the gauge go to full when the sender wire is not hooked to the gauge? If so you have a short in the gauge. Wires hooked up correctly?

 

RMR&C...no, the gauge does not work when sending yellow wire is off. All wires hooked up correctly. I will take it all out again and recheck it all this weekend. But, it is kind of weird because the other cheapy sender did the same thing in always reading full on fuel gauge.

 

Ok I found the problem and not going C R A Z Y!!! The company sent me the wrong sending unit after I told them my problem and bench testing the unit (because it all worked then). But, the sending unit was reading full on the gauge at 30-35% on the "arm" of the sending unit. So, I needed the 35-240 ohms, not the 0-33 ohms. Plus, they sold me a FSU saying that it works on 6v and 12v. I guess not. So then, I bought a new 12v gauge plus a stewart-warner FSU. Problem solved and they are not going to put me away....yet! lol