+ to - conversion

[Bayless]

You definately do not reverse the wires at the gauge. It will not work right that way. If the gauge reads full all the time there is probably a break in the wiring to the tank or a bad ground at the tank. It is hard to verify the voltages but you can pretty easily check the resistances. With all 3 wires disconnected from the gauge, check the following with a simple ohmmeter at the gauge. The readings should at least be pretty close to the following.

B post to center ground post = 162 ohms
B post to T post 61 ohms
T post to center ground post = 101 ohms

Then check the sending unit by measuring the resistance between the wire post and the unit's body. When full it should read about 70 ohms and 0 ohms when empty.

Finally, if all this is about right, check the continuity of the wire between the gauge and the tank. Also ensure that the sending unit is properly grounded to the tank and the tank is properly grounded to the car body. I suspect one of those two is the real culprit.

Also don't forget the Tachometer if it is electric. You do have to change it's polarity and that requires some wire cutting and soldering. If it is mechanical drive, then no conversion is necessary.

Hope this helps.
Bayless

 

[healeyboz]

I think you are correct Bayless, but too late!! I crossed the wires and fried the ground that I was using. I hope the smoke was not the gauge!!!

I will put the wires back the way that I had it but take readings first. The black wires running to the middle post should be grounded right?

 

[jlaird]

Correct and ground comes from the wire from the sender, ohm meter says good.

 

[healeyboz]

Okay, so I had a ground issue at the guage,,,, I think. I hooked another ground to the guages and everything seems to work. The guage jumps until it gets to about 3/4 full. I am on my way to buy some clamps to see if I can get the guage to read differently. Draining the tank.