The Stovebolt Site Forums The Shop Area The Electrical Bay Temp gauge and voltage

Awhile back I upgraded my 1947 1st COE to a 12 volt system. I bought the appropriate Runtz reducers for the fuel and temperature gauge. Both gauges worked fine on the 6 volt system. The fuel gauge works fine on the 12 volt system with the voltage reducer. I fiddled and fiddled with trying to get the temp gauge to work and under no way could I get any reading, period.

I swapped out for the Chevrolet type of gauge with the capilary tube and never looked back.

Yesterday I pulled the dash out for a clean up and started wondering about the temp gauge again. Why would it not work with the Runtz reducer? Yet it still works if 6 volts is applied? I have a pair of GMC electric temp gauges and a few 6 volt senders for them.

Is it possible that the gauge could work without the reducer? I really dont want to fry the gauge attempting something that may not work.

Also, the Chevrolet gauge is barely long enough to work which is probably what started me thinking about the old GMC electrical gauge.

Any insight is appreciated!

Thanks, Jeff

Jeff,

I'm confused as usual. I would assume because of the weird relationship between dash and engine location that your COE did not come with a traditional tube type temp gauge but did come stock with an electric gauge.

This stock electric gauge has a sending unit in the head somewhere, and when you put your voltage reducer in series with the power wire to the gauge that it no longer reads at all, correct!

You didn't stick the voltage reducer in the line from gauge to sender, right. Wouldn't any GMC item of that vintage be built for a positive ground...I don't understand.

Stuart

Stuart, all 41-47 GMCs came with electric temperature gauges and senders. That was one of the differences between Chevs and Jimmys of that style. God knows why, but thats the way it is.

When I first aquired the truck I ran it at 6 volt positive ground. Then changed to 6 volt negative ground. And finally to 12 volt negative ground.

Yes, I did put the Runtz unit inline to the gauge as a negative ground vehicle would be. Same with the fuel gauge. I cant remember as its been months, but I believe when I switched to negative ground, I swapped the terminal connections at the Amp, Fuel and Temp gauges as required.

All parts worked on 6 volt negative ground.

Does that make sense now? My head hurts from thinking about it!

Thanks, Jeff

Jeff,

It does make sense...somewhere along the line I didn't notice your COE was a GMC, my bad! I took the time to reread your post and of course it makes sense now.

I have seen posts here and on the GMC site dealing with the electric temp gauge and senders. They seem to be a tough subject, although they shouldn't be any different than a fuel gauge.

You say it works when a true 6 volts is applied but does not work with the Runtz style reducer...this is weird. My first thought would be to stick a simple, non-solid state (Runtz) volt-a-drop type in there and see what happens. Good luck and let us know if you go up in flames.

Stuart

There have been a few discussions about this with no real definitive answer so I figured Id try again!

I originally tried the normal reducers and they work like crap and have been sitting on the shelf ever since. The Runtz was the way to go and I wouldnt recommend the other type to anyone.

The fuel and temp gauges look absolutely identical. I wonder if the windings are different?

Maybe I should stick a fuel gauge in there and see what happens!

For what little help this may be, when I converted my old 55.1 panel to 12v I didn't think about the possibility of needing to drop the voltage to the gauges so I didn't. They worked great @ 12volts for over 100,000 miles after the conversion. Maybe you don't need the reducers at all.

Thanks for the info Tiny.

Ive heard of people doing that, but at the cost of gauges Im a little leary. I suppose if it doesnt work Im not out anything!

I can always swap back to the chevrolet gauge...