Fuel Gauge on a 41

[TodFitch]

Go, the 1936-48 Plymouths (and maybe 1935?) used a two wire gauge with the indicator working on the heating of thermostatic bimetalic blades. For an additional review of how this is supposed to work beyond what is in the 1936-42 or 1948-54 service manuals you can look in other references. For example there is a short write up on page 650 of my twentieth edition of Dyke's  Automobile and Gasoline Engine Encyclopedia under the title of "Auto-Lite Electric Gasoline Gauge".

Basically the sending unit has a resistor between terminal 1 and terminal 2 that a float actuated wiper blade rides against. Resistance between terminal 1 and ground is lowest when the tank is empty. Resistance between terminal 2 and ground is lowest when the tank is full. Unfortunately I don't have a reference on what the resistance values should be between terminal 1, terminal 2 and ground should be for the various positions of the float.

[Go Fleiter]

no idea, if my 1951 values (from this Forum) are of any help for You:

empty read ist 8 Ohm , full is 102 Ohms

Greetings! Go

[notdavidspade]

I have a service manual, and its just useful enough not to be thrown away.? In my humble opinion, its right up there with a glass hammer.? Let's review the shop manual's procedure for testing the fuel gauge (its in the fuel section of the book).? "(1) Select a spare tank unit known to be in good condition."  Sure... just let me pull that out.  Also, is it just me, or does the table on step 10 make no sense at all.

The ground suggestion is a good one.  I attached a ground from the tank to the frame and the fuel guage sprug to life.  Since its a woodie, not much grounding the tank otherwise.  Now that my guage has life, I'll look at the contacts on the circuit breaker.  (manual says dirty points will cause a fluctuationg pointer, see.. something useful comes out of it every once in a while.).  Thanks for the help guys!

[plym_46]

Try testing the sending unit's ground with a jumper wire.  go from one of the screws holding the sending unit to the tank and go to known good ground on the trunk floor sheet metal.  If that works, then attach a permanent wire.  Most electrical problems with 6V systems are due to incomplete grounds causing extra resistance in the circuit, and since the fuel gauge works by measuing varying resistance through the winding in the sending unit, you can see where this will foul up the gauge reading.

You may also consider running a ground wire from the firewall to the frame.  You might find a lot of stuff working better. The other thing to check is that there is no inadvertant grounding at the gauge.  My defroster duct fell away from the difuser, and the wire stiffener in the duct contacted one of the terminals on the rear of the gauge and caused my gauge to do all kinds of things, other than indicate fule level.

I just had a deal on my truck (another orphan brand) whee I could not get my rear lights to work.  The test light showed the circuit being completed to the frame when I tested but I had to actually ground the lamp housing with a jumper to the frame.  A wire conected from a bed crossmember to the frame solved the problem.  So even with metal to metal contact and with new hardware connecting the bed to the frame it was iinsufficient to complete the ground circuit.

[John Hendricks]

U need a service manual.  I can't recall whether it is under Electrical things or Fuel system but the specs for the gauge are in there.

[notdavidspade]

Hello all.
I'm trying to figure out my fuel gauge.  I filled the old girl up with gas and the needle stayed on empty.  I get the following numbers off the sending unit.  between the two wires, 24 ohms, wire 1 to ground 3 ohms, wire 2 to ground 18 ohms.  If I disconnect one wire, the gauge reads about 3/4 full.  I've tried reversing the two wires without luck and even tried just connecting them together without getting the needle to move.  Anyone have any ideas or know how this thing is suppose to work?  Thanks!
Stephen