Fuel gauge sending unit: Ohms ??

[Go Fleiter]

Hello all!

Maybe I need a new 1 wire sending unit for my 51 P 23; 6 V,.

How can I evaluate my existing unit:

Can anyone tell me how much Ohms the sending Unit should have between full and empty?

Thanks! Go

 

Edited September 29, 2019 by Go Fleiter

[Sniper]

Pretty sure it is 73-10 ohms, empty to full.

[chrysler1941]

This from DeSoto shop manual. There is a full page about diagnosing the fuel gauge. Do you want a copy or is this enough?

[Go Fleiter]

Thank You! Perfect!

 I have nearly ther same diagram in my Service Manual, but no ohms in it!

Very helpful!

Greetings from Düsseldorf!

Go

[50Dodge]

I am trying to figure out the same thing. I show 6V reading on my SW terminal. I assume if I test GA wire and see zero Ohms then my unit would be bad. Not to infringe on Go Fleiter post.

[Sniper]

never mind. got confused

Edited October 1, 2019 by Sniper

[chrysler1941]

8 hours ago, 50Dodge said:

I am trying to figure out the same thing. I show 6V reading on my SW terminal. I assume if I test GA wire and see zero Ohms then my unit would be bad. Not to infringe on Go Fleiter post.

yes GA is hot. originally -6v. Zero Ohm is same as grounded. Ground GA at gauge. If it reads Full, gauge ok.

Ground terminal sender in trunk. IF same, then connection to gauge ok, 

Measure Ohm at sender to ground. Try tank then frame as ground. Typical error, tank not grounded due to corrosion etc.

[Sniper]

Ok, I pulled the sender out of my 51 Cambridge today. measured the ohms, 90-9 is what I read from one extreme to the other.  So that Desoto FSM is correct.  My FSM shows that picture but not the ohms and I could find no reference in the book to the sender specifications.  Incidentally, it has a cork float.  Do those things ever get "waterlogged"?

[DJ194950]

See post #3 above -the ohms range is on that picture.

 

Good luck- your sender seems to be good!

 

DJ

[Mopar-Boy]

I know this is a very old post but this is the type of gauge and sending unit I seem to have in my 33 Dodge DP6.  If that is the case, can I run 12V to it?  It seems like the system is just looking to "mate" the resistance from the sending unit and the gauge.  So my guess is the voltage shouldn't matter?

[TodFitch]

The gauge is designed to work over a range of voltages because and automotive electrical system varies a lot, especially one in a 1933 with poor regulation.

 

But doubling the nominal voltage from what the original was designed for could well shorten the life of the dash unit.

 

Personally I’d put a regulator on the power supply to the dash unit to bring it down to around 6v. Even just a reducing resistor would be enough.

 

What I have done on my 33 Plymouth was to hide a 6v+ to 12v- converter under the dash for the couple of 12v modern things I wanted and left everything else, including the fuel gauge, on 6v.

[Mopar-Boy]

Thanks TodFitch.  I used a multimeter and found 0 volts on SW.  Took off all the wires and found 0 ohms between the two posts, GAS and SW.  So... pulled the meter out.  When I rewired the gauge, loosening the nut holding the wire onto SW, it moved the post/backing.  The back plate has holes in it just slightly larger than the posts/screws and it is held in place by notches that mate on the gauge and plate.  VERY shallow notches and easy to misalign.  So pulled it apart and reassembled VERY carefully and now everything works GREAT.  12V system w a digital volt reducer to 6V wired to SW.  It's a bit bouncy but not bad.