Fuel gauge

[Veemoney]

Jgreg, 

Maybe one of the other members here will recognize it from the picture. It does appear to have some markings or numbers that may be visible. I usually take some close-up pictures then view them on the computer where I can zoom in to confirm numbers and markings. Once I have the numbers, I google to get mor info on the part.  I tried zooming in on your picture but could not make anything out. Also a shot of the backside of the gauge will help confirm the type of gauge and hook-up. 

[jgreg53]

There's some markings on it but a lot of it is rubbed off. Is it not a part that's on all p15's? The heating elements are not heating. 

Edited September 2, 2022 by jgreg53

[Veemoney]

16 hours ago, jgreg53 said:

There's some markings on it but a lot of it is rubbed off. Is it not a part that's on all p15's? The heating elements are not heating. 

Without any further pictures or info I would be guessing and that is not a good idea since the fuel gauge is a fairly delicate piece. I not sure what the round red part is myself or it's function without further information. 

 

 I did a quick search here and found a wiring diagram for the P15 which does not appear to show the red part. That doesn't mean it is not required if say you are running some other modification or power different from original. 

 

The fuel gauge depicted in the diagram has a terminal 1 & 2 which would be the old-style gauge. If you can confirm your gauge has a 1 and 2 terminal designation it should then also have power from the ignition  switch to the IGN SW terminal. This is why I requested a picture of the back of your gauge which you have not provided.

 

 

Edited September 3, 2022 by Veemoney

[Sniper]

If the red part is actually part of the fuel gauge assembly I doubt it's show up in the schematics.  Looks like a capacitor/condenser to me.  Might be something someone added for noise purposes?

 

So I looked up the part number, 1149325 I believe.

 

Found an NOS one on EBay, no red thing on it.

 

https://www.ebay.com/itm/363906516788

[jgreg53]

It is very delicate.  Like a Swiss watch

[Veemoney]

Sniper, makes sense. Was hoping you or someone else may have seen one before

 

Jgreg,

 I also looked at gauges first and did not see any with the red part so looked at the wiring to see if it would show any additional components. What I did find today is the possibility it could be a radio resistor as called out in my Motors manual, 1 version of the fuel gauge had a provision for it though I don't know that I see any provision on the back of this gauge.

 

My suggestion would be to bench test without the red part using the 6v battery from the car and starting with the old fuel sending unit hooked up as shown in the second picture. Third picture shows the numbering on the sending unit that corresponds with the terminals on the back of the gauge. 1 goes to 1 and 2 goes to 2. this assumes the sending unit resistor is correctly installed with the small end at number 1.

 

1. Make sure the sending unit flange is level and grounded to the battery. I had a tough time getting a good ground at the flange.
2. Carefully clean the points of the gauge by pulling bond paper through the closed set
3. Gauge does not require ground but should be upright as if it were in the dash so the balance is correct. 
4. Set float on gauge up near the position it would be when the tank is full
5. Use jumper wires to connect numbered terminals first 
6. Hook up power with jumper wire from 6v battery to Ign SW terminal on gauge.
7. Give it a minute or 2 to warm up and start moving to full if it moves great
   1. If not check gauge ground and try it at a couple positions mine was touchy
   2. Move the float 1/4 inch to see if this gets a reaction
8. Next position the float as if the tank was empty. You can measure the gas tank from the flange to the bottom of the tank to get the position. and see if the gauge responds correctly.
9. If the gauge is responding but not accurately for the position of the tank float try hooking the 1 terminal wire to the 2 terminal and the 2 terminal to the 1 terminal
10. repeat steps 4-8 if this does not correct the issue replace the old sending unit with the new sending unit and start testing from step 1 for the new sending unit

 This above testing assumes the gauge is good and the tests are quick and easy when done on the bench. if you cannot get good results then the gauge can be tested separate from the sending unit.

 

 

 

 

 

 

[jgreg53]

I may have stumbled on to something. I hooked the gauge up without the red doohickey. The needle moved. It stopped at a quarter tank but at least it moved. The guts inside the thing are so delicate. Any movement can change the the reading.

[SteveR]

14 hours ago, Sniper said:

If the red part is actually part of the fuel gauge assembly I doubt it's show up in the schematics.  Looks like a capacitor/condenser to me.  Might be something someone added for noise purposes?

I'm wondering if it is a capacitor used to smooth out the reading from the sending unit in the tank. Thereby being an add-on by someone.

Edited September 4, 2022 by SteveR

[jgreg53]

The reason all this started. I had taken the gauge out the first time because the reading was erratic. In my fumbling to put it back in I broke the wire off the capacitor. I had been trying to solder it back on. I probably ruined it in my attempts if it wasn't bad already. The inner workings of the gauge are kind of a mystery to me. The heating elements somehow cause the needle to move. 

[Sniper]

What happens, near as I can remember, is that as the bimetallic strips heat they bend.  They bend because those strips use two different metals in their construction and have different rates of expansion.  the variable resistor that is part of the sending unit controls the current flow thru the strips and that controls the amount of heating and thereby the amount of bend in the strips.

 

 

[DonaldSmith]

Yep,, it's what the Service Manual calls a "bi-metallic gauge".  It merited one-and-one-half pages, to 'splain how it was supposed to work, and how to service it.  

The reading gas was a sort of tug-of-war between the two bimetallic strips.  I suppose it was an attempt to even out the sloshes in the tank. 

 

Chrysler gave up on it and went with an electro-magnetic type.  Cheaper, less prone to trouble, and using one less wire.   

Edited September 4, 2022 by DonaldSmith
typo

[jgreg53]

Magic 

[Sniper]

26 minutes ago, jgreg53 said:

Magic 

lol, when I was learning electronics in the Navy that term was used regularly to "explain" how things the instructor didn't understand worked.

 

All it really did was make use dig into it on our own time to figure it out. 

[kencombs]

19 minutes ago, Sniper said:

lol, when I was learning electronics in the Navy that term was used regularly to "explain" how things the instructor didn't understand worked.

 

All it really did was make use dig into it on our own time to figure it out. 

Or, FM.   Which I'm sure you can figure out with your Navy vocab.

[SteveR]

SHAZAM! = Gomer Pyle

[Sniper]

5 hours ago, kencombs said:

Or, FM.   Which I'm sure you can figure out with your Navy vocab.

 Well it was PFM actually, but I was cleaning it up, the P means pure, lol ?

[jgreg53]

Well, I put the gauge in the dash. Hooked up the wires. Turned the switch  and it started smoking. Turned off the switch. Investigated, found a bare wire grounded to the metal dash. It fried the heating elements.  So much for that. Would a 6 volt gauge for a tractor work?

[Veemoney]

The harsh truth is there is at least 1 bare wire maybe 2 showing here screaming for some attention. Consider it the price of a lesson learned. It could have been worse.

I hate plastic insulators on lugs, heat shrink tubing is cheap reduces the stress at the connection. 

2 hours ago, jgreg53 said:

Hooked up the wires. Turned the switch  and it started smoking. Turned off the switch. Investigated, found a bare wire grounded to the metal dash. It fried the heating elements.

[jgreg53]

I took the gauge completely apart hooked it up. I saw how it worked. As the bimetal strips heat up they bend and touches the gauge pointer and moves it. The straps heated and bent but missed the pointer as if the blades weren't long enough. 

[Marcel Backs]

The wiring is indicative of the problem at hand. Get a copy MOTORS auto repair manual to get a better idea on how your fuel gauge works and can be troubleshooted. The manner in which the fuel level indicator system on old mopars was designed was far from ideal leading to finnicky operation. The rusty looking device you are asking about is probably a filter capacitor which is many decades beyond it's best before date. Check out the topic lookup since I have posted all the pertinent data on this subject with the help of colleagues on this site.

[jgreg53]

I repaired some of the wires, replaced some used heat wrap to cover the connections.

[jgreg53]

I have an aftermarket fuel gauge. It's supposed to be universal.  I also have a 6 to 12 volt converter. I hook the converter up to the battery and it shows 12 volts.  When i get the fuel gauge hooked up and then try to attach the ground wire to the battery, the ground lead starts heating up to the point that the insulation starts to fry.  What am I doing wrong?  Do I need to hook the converter up at the switch?

[Dodgeb4ya]

Supplied with factory radio ....for noise supression.

I posted a pic of a nos one a few years back and now again...

1946-48 upper line Chryslers usually  always have then installed on the back of the fuel gauge.

Edited October 18, 2022 by Dodgeb4ya

[jgreg53]

I found and bought an original fuel gauge from amsobsolete. NOS. 70 dollars. Waiting for it to be shipped. 

[jgreg53]

I finally got the NOS fuel gage. Hooked it up. I have 6 volts going to the ignition connection.  The elements are not heating. Does it need to be grounded some way?