Alright I put the mustang tank in my 51 a few years ago and i am having inaccurate reading on my gauge. Does anyone know the ohms that it reads when it is full and empty? Are their variations? it is a 1970 20 gallon tank.

 

What voltage are you supplying to the gauge?

 

1970 Mustang sender should be 73 ohms empty, 8-12 ohms full. Good luck. If you google this topic you'll get a ton of hits. You're not the only one trying to figure this out.
Fuel Level Gauge with OEM Sender - Auto Meter Tech Tips:

 

see thats what P*sses me off. I bought a really nice set of woodward gauges. NOT CHEAP, but I wanted an electronic speedo, anyways I asked the guy what the correct one was for my mustang tank "oh you need the 73-10 ohm gauge" so it must be the wrong one or messed up.