Classic/Antique Car Repair: 69 chev pickup 1/2 ton two wheel drive, turning the key, gas tank

Question
the gas tank is behind the seat and the sending unit only has one wire, were does the wire hookup behind the dash?when turning the key on the gauge gets power but there is no wire going to it from the sending unit

Answer
You know, I have actually repaired this problem in the past, but right now the answer escapes me. It is a grounded system and the wire passed thru the gauge. But I seem to recall something I didn't expect when I worked on this.

I will have to check some older manuals, but they are not at my disposal this morning, they are in storage. If I get this soon, I resend.