Dual Tank Valve Ground

[Ronno6]

Seems like a simple question:
1984 C-10 gas engine.
How is the dual tank switching valve grounded??

Only thing I can see is that the valve is grounded thru the gauge sending unit??
Doesn't make much sense to me.
But I have pored over the schematics ans I can see NO ground wire anywhere.....
When testing the power to the plug, I can get a 12v reading between one green wire and ground
when the switch is pushed in one direction, but can only read about 6v on the other green wire when the switch is pushed in the other direction....

Or, do the 2 green wires supply power and ground, but reverse polarity when the switch operation is reversed??

Stumped......

 

[SirRobyn0]

So the switch changes polarity. IIRC there are 2 wires that actually operate the switch, the rest of the wires are for the gauge. The dash switch changes the polarity of the switch wires. Where the actual ground is I don't know.

 

[Ronno6]

So the switch changes polarity. IIRC there are 2 wires that actually operate the switch, the rest of the wires are for the gauge. The dash switch changes the polarity of the switch wires. Where the actual ground is I don't know.

Be that the case, then for one tank, one green wire is 12v + and the other is ground, then they swap for the other tank position of the switch... I will check that out.
But, if true, I should be able to read 12v from one green to ground when switch is pushed up, and between the other green wire to ground when pushed the other way.
I do not have those readings...

 

[Ronno6]

So the switch changes polarity. IIRC there are 2 wires that actually operate the switch, the rest of the wires are for the gauge. The dash switch changes the polarity of the switch wires. Where the actual ground is I don't know.

You are correct.
I was able to see +12v at the harness when the switch was pressed up, then -12v when pushed down.
But, then the voltage went wacky...like 3 to 4v...each direction. I did hot wire the valve and it moves in both directions.....a good thing. Just not when I try with the switch. Actually it DID move...once, but nevermore... But, maybe I should replace the switch and the valve as long as I have them out ??

 

[SirRobyn0]

You are correct.
I was able to see +12v at the harness when the switch was pressed up, then -12v when pushed down.
But, then the voltage went wacky...like 3 to 4v...each direction. I did hot wire the valve and it moves in both directions.....a good thing. Just not when I try with the switch. Actually it DID move...once, but nevermore... But, maybe I should replace the switch and the valve as long as I have them out ??

Honestly that sounds like a switch problem to me as well, but given the importance of a properly functional tank switch, yes I would opt to replace them both.

 

[Ron Sebastian]

Can't over stress the importance of a good ground for the switch, the valve, and the fuel pumps.

 

[Lowered87]

1973-1991 Dual fuel tank systems theory of operation - The 1947 - Present Chevrolet & GMC Truck Message Board Network

1973-1991 Dual fuel tank systems theory of operation The 1973 - 1987 Chevrolet & GMC Squarebody Pickups Message Board

67-72chevytrucks.com

Not that I am promoting another forum but here is a link for lots of info on dual tank wiring

 

[Lowered87]

Just remember there are different switches depending on the year of your truck. Also the big black wire off of the sending unit needs t be grounded to the frame.

You must be registered for see images attach

 

[SirRobyn0]

This is a pretty old thread, but yes the switches are different and they work quite differently and are not interchangeable at all.

 

[ali_c20]

If you're replacing the valve the switch must match the valve.