Gas gauge wireing

[blackchevy3de]

I have a 39 ford sedan it 12v neg ground do I have to change the 6v pos ground gas tank sender to make a SW 12v gas gauge work, if not what do I need to do. thanks guys

 

[19Fordy]

Yes, you need to change the sending unit in the tank to 12V. Get one that is compatible with your 12V neg. ground SW gas gauge. If you do a search for "12V gas tank sending unit" info. such as the following w appear.
http://www.fordbarn.com/forum/showthread.php?t=198896&highlight=12V+gas+tank+sending+unit

 

[Kahuna]

Or, you can buy an inexpensive resistor & install it.
I did that for my 39 coupe. Wasn't perfect, but worked OK.
Not perfect, meaning not perfectly accurate, but very close.
Jim

 

[blackchevy3de]

jim is what you are saying is with this resistor I can use the 6v pos grd sender with the sw 12v neg grd gauge, car is 12v. if so do you have a part number, would really help. thanks jim

 

[koates]

Your 12 volt Stewart Warner gas gauge requires the matching SW tank sender. The gauge requires a variable resistance ohms reading from the sender unit which matches the gauge requirement exactly and nothing else. Other gauges and sender units may have different resistance specifications to your SW gauge. Messing with resistors and non matching components is a total waste of time and money. The 39 ford original 6 volt gas tank sender works on a totally different principle to the SW variable resistance type and should not be used with the SW gauge. Get the correct SW sender unit and adapt it to your ford tank. Do you still have the original Ford gas gauge, because it can be used in your car provided the ignition power supply to the gauge is reduced from 12 volts to 6 volts using a voltage reducer. It would work OK on negative ground system with the original Ford sender unit. Regards, Kevin.

 

[rotorwrench]

If you check out sending units available, you need to know what Ohmic values the gauge you have works with. Companies that make the rheostat type senders make them in values that work for the various different manufacturers. I believe SW uses 240 to 33.5 Ohms values between full and empty. It may also need to be adapted to work in the old Ford tank bung.

As was mentioned, The King Seeley sender will not function with anything other than a matching King Seeley gauge since it is not rheostat based. It uses a current regulated system with heating coils & bi-metallic switches.