Classic/Antique Car Repair: Gas tank sender unit to fuel gauge wiring, fuel tank level, camaro subframe

Question
Dear Mr. Sears, First of all, I`d like to express my sincere appreciation for your extremely thorough and informative answers in the past. This question deals with a wiring problem that has bothered me for quite some time, I`m hoping your answer will ease my mind. I have been working on a `56 Chevy pickup on and off for years now, an it`s finally time to complete it to the roadworthy stage. The truck is a very mild street rod, using `74 & `75 Camaro subframe, and entire running gear including engine, transmission, drive shaft, and differential. I`ve also removed the original dash and replaced it with a `74-`75 Camaro dash with the original Camaro instrumentation, and full wiring harness. I have everything wired, except the fuel gauge wire to the original `56 Chevy tank and sender unit. I`ve checked the wire from the fuel gauge instrument panel for any possible voltage, and it appears to be a ground wire. I had read a while back, the fuel gauge and sender unit work on some sort of variable ground system. If I complete the wiring, is there any possibility of positive current running to the tank sender unit creating sparks inside the tank? I`ve also read the original gauges from early Chevy pickups used a different resistance rating than that of later Chevrolet models, which would result in incorrect fuel tank level readings on the `74-`75 Camaro instrument panel. The truck is nearly roadworthy, and I had been considering never finishing the wiring due to this issue, and the possibility of a kaboom, with the cab mounted tank being directly behind the seat. Thanks in advance for your advice, and informative answers! Sincerely, Dave

Answer
The fuel gage system is designed to put battery voltage into one side of the dash unit, through two magnetic coils and the other side of the dash unit is then connected to the sender unit in the fuel tank. The sender is grounded through the tank or a separate wire to the frame and back to the battery. The amperage reaching the tank is very low due to the resistance in the dash unit. The stock sender may work but if it does not chevs of the 40's sells senders that will work in your tank. www.chevsofthe40s.com