The Stovebolt Site Forums The Shop Area The Electrical Bay 6V vs. 12V vs. Fuel Gauge

Still new to the site and new to restoring my 55 GMC series 2 that my wife got from her father. In 1983 he rebuilt the truck, and put in a Chevy 350 from a '77 blazer.

I've now been through 3 OEM fuel gauges and have been testing them using a standard 12v battery. I have not had a chance to pull the sending unit out of the tank yet.

My question (and this may be stupid) - but since the fuel gauges were originally made for a 6V system, will they even work on a 12V system? It just doesn't make sense that all 3 of my gauges are bad.

If the truck originally had a 6 cylinder engine it originally had a 6v positive ground electrical system (GMC had standard 6v positive ground in 6 cylinders trucks through all of 1955). If the truck was originally equipped with a V-8, it would have had a 12v system. ( see page 20)

How many cells in the battery?
Do the lights work?

The truck is a rebuild, it now has a V8 with a 12v system. It originally had a 6 cylinder with a 6v system.

3 OEM gauges? For a 6v 6-cylinder or for a 12v 8-cylinder?

I've tested 3 gauges, all on a 12v battery and none seem to work. That led me to thinking that maybe the gauges only work with a 6v system. My next step is to buy a 6v battery from wal-mart and test the gauges with that.

http://www.flickr.com/photos/71945287@N03/8505891142/in/photostream/

the way to initially test the fuel gauge starts with resistance checking of the sender, if you haven't included the sender in your testing, how did you test them? - you've likely burned out the 6V positive ground gauges using 12V directly to neg ground on them

Bill

You'll need an adapter to use the original - to reduce the 12v to a 6v. They are available for around $15 from many parts suppliers.

With a GMC you can just get a 12 V gauge from a later truck. I put one from a '59 in my '54.

GMTk
I have the same truck....I used a resistor I got from Patrick's on my fuel gauge. Reduces the voltage from 12 to 6 volts.
http://www.patricksantiquecars.com/articles.html

But Cletis has the right idea, if you can find one!
Oh, and pull out that fuel sender, I'll bet you find it's corroded.

Thanks Marc and tclederman - part ordered. I also plan on pulling out the sending unit and checking it from there. My wife thinks I'm crazy for all the work just to be able to use the original gas gauge....

You state you have been through 3 OEM fuel gauges. If you have not, don't buy 6V fuel gauge, purchase a 12V replacement. Then no resistors, no scabbing or bandaids.

See:http://www.americanclassic.com/asp/dyncatv2.asp?which=amclsall&p1=initial&p2=Speedometer+and+Gauge+Items&iyear=1955&ytype=to&exyear=1955

Thanks to all for the help. I send all the gauges off to Bob's Speedometer repair in Michigan. All 3 were dead. He fixed one and it's not installed. Replacing the sending unit today so I'm hopeful that will solve the problems. Thanks again for all the advice and help. Not sure what I would do without this forum.