Simple gas gauge sending unit question.

[oldschool47]

Hello all!

Well... I ran out of gas. And I think I know why. NO GAS!

I have a new gas tank and what I believe is a 6v/12v sending unit.

My car is a 12v conversion.

Car will read super full at the gauge and will read at 1/2 full, actually be dead empty.

There are three leads to the gauge which from the harness I am 100% sure are properly hooked up.

Two leads up top one on bottom.

Which lead do I need to reduce the voltage of to get my gauge to read correctly at the dash? I am positive I am so close to this solution.

[oldschool47]

Sorry having trouble uploading the rear of the gauge...and of course my shop manual is missing.

Edited November 12, 2014 by oldschool47

[TodFitch]

Assuming P15 per your signature: There should be four wires attached to the three studs on the back of the fuel gauge:

 

1. A blue wire providing power from the ignition switch

2. A brown wire attached to the same stud to provide power to the starter switch.

3. A Black and yellow wire from the sending unit attached to a stud that looks like it might be labeled "2"

4. A blue wire from the sending unit attached to a stud that looks like it might be labeled "1".

 

Both wires from the sending unit go through a connector and the color call out is on the side of the connector toward the sending unit. I am assuming the colors are the same from the connector to the gauge unit.

 

There is a table in the service manual that shows what will happen if one or the the other or both wires to the sending unit are grounded or open. One entry says that if it reads full when full, 3/4 when half full and 1/2 when empty then wire #1 is open.

[Don Coatney]

Pictured is the back of the gas gauge I recently removed from my P-15.Clearly shows how the gauge is labeled.

 

 

[oldschool47]

Thanks guys this clears up a ton!  Going to my storage unit to locate my manual.

 

So it isn't so much that my fuel gauge may be getting the wrong voltage but my #1 wire could be open?

 

Thanks again I'll try to reground them to the frame and see if there is a difference.

 

Also if I am reading  WAY FULL instead of just F I probably have a grounding issue not a voltage issue?

 

Thanks again Tod/Don!

Edited November 12, 2014 by oldschool47

[TodFitch]

You might be having a voltage issue too. The unit works by heating up elements in the dash unit based on current passing through the two circuits to the sending unit. With a higher voltage you will be running more current through it and heating it up more. My guess is that it will work, for a while. Until it is damaged by too much heat. You should consider putting a voltage reducer on the input to it.

[Plymouthy Adams]

the two wire sender and gauge has a built in 5 volt voltage regulator as part of the gauge itself...with12 volt operation you will often see a bit of flicking needle movement...due to the rapid heating and cooling (opening and closing of the contacts) as the regulator operates at a faster cycling..

Edited November 12, 2014 by Plymouthy Adams