Help with my stock gauges?

[Sam_Fear]

Anyone know much about hooking up the old gauges?

Trying to use the stock fuel and temp. gauges. I have the old temp sender, but am using a '85 fuel sender. As far as I found the '48 Olds was 6v positive ground. I have a 12v to 6v reducer installed. The gauges are 2 coil types.

Here's the thing: With gauge cluster removed, I can hook up power and jumper a ground at the dash - it works. But as soon as I touch the gauge cluster to the dash, even though that is what the ground is jumped to, the gauge goes dead?

I'm wondering if it's because the gauge was set up for positive ground? I don't seem to be getting any backfeed through ground - maybe 5mV at worst. How sensitive are those gauges to voltage?!

 

[rustybeercan]

I'm wondering if it's because the gauge was set up for positive ground?

Sam,
I think most American cars were pos ground until the mid 50's!

Beercan

 

[Old Iron]

If the battery in the car is negative ground, you'll have to switch the wires on the back of the gauges from one post to the other for them to work as positive ground [S
The 85 fuel sender is 90 ohms and is going to need to be the same ohms as the original 6v gauge which I think is 30 ohms for it to work.
You'll have to switch to a GM up 1964 0-30 ohm sender. From 1965 they went to 0-90 ohms.

Jim

 

[RPM]

Classic instruments may have some info on their web site.

 

[rsfyj]

sounds to me your gauge needs to be above ground with the jumper. when you set the dash it is no longer above ground potential cause your dash is grounded. Example old Table radios all AC were set above ground meaning they were isolated from real ground. If you actually grounded the chassis to the actual circuitry it would short out. Try using an insulator between the dash and the gauge if not try to ground it with a small capacitor 12 volts rating a little ceramic disc type or a high resistance resistor between the gauge and dash to isolate it and keep ground potential.and keep the ground jumper and see what happens