Fuel gauge not working

[Mertz]

I have 51 ohms between terminals on the sending unit with about 1/4 tank of fuel. I have power to the gauge at all three terminal with switch on. The bottom terminal is not as bright as the top two. I have continuity from the gauge to the sending unit. The tank is well grounded. Grounding #2 wire gauge goes to full. Does the sensor wire on the sending unit go to terminal one or two?

[bacelaw]

29 minutes ago, Mertz said:

I have 51 ohms between terminals on the sending unit with about 1/4 tank of fuel. I have power to the gauge at all three terminal with switch on. The bottom terminal is not as bright as the top two. I have continuity from the gauge to the sending unit. The tank is well grounded. Grounding #2 wire gauge goes to full. Does the sensor wire on the sending unit go to terminal one or two?

 

 

On the 41 plymouth version I have, all you do is run a ground wire from one of the mounting screws on the sending unit to the frame - then the gauge works great...

[Mertz]

Checked the ground at the sending unit and it’s good. Added a jumper from ground to the sending unit and tested again. Good ground. Grounded the sending unit terminal and the gauge goes to full. Grounded the ground terminal on the gauge to the battery. Power to the gauge. There was one point where it didn’t go completely to full but and fluctuated near full. 

[bacelaw]

22 minutes ago, Mertz said:

Checked the ground at the sending unit and it’s good. Added a jumper from ground to the sending unit and tested again. Good ground. Grounded the sending unit terminal and the gauge goes to full. Grounded the ground terminal on the gauge to the battery. Power to the gauge. There was one point where it didn’t go completely to full but and fluctuated near full. 

 

Did you run a ground from a mounting screw on the sender (not the sender itself) to the frame?  On the 41 gauge, there are only 2 wires going to the gauge.  Neither of them is hot and neither is a ground.  A ground wire is required from the sender mounting screw. .at least that's my memory from a couple years ago. 

[Mertz]

I did run a jumper from the mounting screw on the sender to a good ground. Mine has two wires from the sender but 3 on the gauge one being power from the ignition switch which I confirmed with the wiring diagram. This gauge apparently is a two sided gauge with one side counter acting the other side. 

[Mertz]

My sending unit doesn’t look like the OEM unit. It has an adjustment for a deep tank and shallow tank. First pic is the unit I bought with the supposed correct sending unit. The unit I bought with the tank has 6 screws while the OEM has 5 screws  

Edited August 24 by Mertz

[Sniper]

Ok, it really depends on what year we are talking about.  Sounds to me like your gauge is the older thermostatic type

 

And it appears your aftermarket sender is not the proper type for your gauge.  But wait, we already covered this?  You have the wrong sending unit.  The one you need does not use resistance, per se.  It uses current flow thru the gauge to make it deflect properly.  Later ones use voltage levels to deflect the needle.  You either need to replace your gauge with one that will work with your sender or replace your sender with one that will work with your gauge.  I recommend going with a mopar specific vendor such as Bernbaum or even MoParPro if there is no other source.

 

I think the part number you need is 591146, not cheap.

 

https://hiltopautoparts.com/product/nos-mopar-fuel-tank-sending-unit-1939-41-dodge-fargo-plymouth-trucks/

 

https://www.moparmall.com/MoPar-PN-591146-Fuel-Gauge-Sending-Unit-p/803-086.htm

 

https://www.ebay.com/itm/176497837693

 

 

 

[bacelaw]

1 hour ago, Mertz said:

My sending unit doesn’t look like the OEM unit. It has an adjustment for a deep tank and shallow tank. First pic is the unit I bought with the supposed correct sending unit. The unit I bought with the tank has 6 screws while the OEM has 5 screws  

 

 

I may have an extra sending unit if you need one.   Just send me a PM, I'm sure we can work something out. 

[Mertz]

All those sending units are 5 holes and my tank is 6 holes. Yes this is apparently a thermal unit. Will a later gauge fit in my dashboard?  Maybe I can hide a working unit in the glove box and keep the old one for originality. I was sold a tank and sending unit specific for my truck. 

[Sniper]

25 minutes ago, Mertz said:

I was sold a tank and sending unit specific for my truck. 

 

You were sold the wrong sending unit.  Tank too if it uses a 6 hole sender.

 

What you got is something that will fit and may work, for the most part, as long as you don't need a working stock fuel gauge.

 

You could probably put an aftermarket fuel gauge on the bottom of the dash in a single gauge mount.  It would work, if you get a gauge compatible with that six hole sending unit.  If you are still a 6v system though, you might find it an issue  to get a gauge that will work on 6v positive ground.

 

 

[bacelaw]

1 hour ago, Mertz said:

All those sending units are 5 holes and my tank is 6 holes. Yes this is apparently a thermal unit. Will a later gauge fit in my dashboard?  Maybe I can hide a working unit in the glove box and keep the old one for originality. I was sold a tank and sending unit specific for my truck. 

 

Who sold you the tank and sender?  

[Mertz]

I understand that thermal gauges are unusual. Here is what I bought.

[Young Ed]

Supposedly the 39-47 truck vendors have a sending unit that replaced the 2 wire style with 1. 

[Veemoney]

Mertz, 

 

The auction you posted shows Tanks Inc. tank "39DP-T" and when I looked up that tank part # at Tanks Inc website it states it uses standard 5-hole senders. 

 

They even provide the bolt circle and spacing of the 5-hole flange. They did not send you the 39DP-T tank because it would of had 5 holes just like it shows on the 3rd bullet above in blue. Important to make sure the details of what you purchased matches the delivery.

 

Now for options to get you going:

1. You likely missed your window on E-bay to dispute the item is not as described but maybe you have some room to negotiate since they sent the wrong tank.
2. You could go for an aftermarket gauge and mount under the dash as suggested but I would not waste my time or money on adding another wrong part to the truck.
3. In this situation I would right the wrong you have and get a 5 hole sender made for the thermostatic gauge that you have in your truck. 
   1. I would not buy any of those high dollar ones that Sniper linked with cork floats that may not last with todays gas or the prices they are charging when Andy Bernbaum sells the one you need for $63 + 11.95 shipping and about 5 bucks tax. Link provided again for you. For 1939-1947 Dodge Truck Fuel tank sending Unit | eBay
   2. Now you have to pull your tank anyway. I would weld up the holes and drill it for a 5 hole sender or make an adapter but for you I see Tanks Inc. sells a bolt in adapter to do just that. It goes from a 6 hole to a 5 hole and looks like about $30 bucks which I would hope someone who made the mistake would send it to you for all the trouble they caused you. Link for adapter here Ford 6 Bolt to 5 Bolt Fuel Sender Adapter (tanksinc.com). 

 

I hope this helps get you going.

[Mertz]

When I bought the unit it said it was correct for my truck. I probably should have done more research to make sure it would fit. The tank fits fine. I did tell the supplier that this forum said it was the wrong sending unit but they insisted it was correct for my truck. I will try to get some help from them but I’m not confident it will work. I will see if I can gat the adapter and new sending unit. 
 

Thanks everyone for the help on this. It’s a great forum and I could not have done what I have on the truck without you. Hopefully on the road soon. 

[Mertz]

I have written the company and will see what they do. I can live with the adapter. I hope that they will provide both the adapter and the correct sending unit. I recently installed the bed on the truck so tank removal will be a little more difficult. 

[9 foot box]

   The sending unit that DCM Classics sells is similar to what you have. Their installation instructions says if it doesn’t work with both wires connected, leave #2 wire connected to the center post, ground the other terminal to the frame and leave the #1 wire disconnected. 

[Mertz]

I tried it but it didn’t work. That terminal is already a ground and grounded to the tank. I was hoping. I’ll let you know what supplier has to say. It is clearly not the correct tank or sending unit. 

[Mertz]

I have mud on my face. I assumed that the sending unit bolt pattern was the same as the inspection cover plate pattern. It actually does have five holes. The sending unit is still wrong and I sent the supplier a picture of mine plus a diagram from a motors manual on how the sender works and how it is wired. They say their unit will work for my year truck but they don’t say only if it has the right gauge. 

[Mertz]

Talked to Tanks Inc and they told me to ground the sensor at the ground wire then hook up the sensor to one of the other wires. One should provide a reading. It did but it was hard to see much movement since it went just to empty with 1/4 tank of fuel. I guess it’s working but I’ll add more gas and see if I get a better reading. I might have not installed the sending unit just right. 
 

Thanks all for the help. 

[Veemoney]

Happy to hear you had the correct tank and that the sender they provided may work with the thermostatic gauge. I hope you took the time to cut an access hole to allow for adjustments of the sender if needed and future access as someone on here mentioned it took a few adjustments to dial it in for him.

[Plymouthy Adams]

it the sender is not dual tapped, ie. each end of the 30 ohms coil with the wiper tracking both ends to ground simultaneously, it will never read correct....your gauge if stock must be pulled in both directions at the same time...

[Mertz]

This is 73-10 ohm universal sending unit. It is working although very slowly. I got a reading of between 1/8 and 1/4 which according to Tanks Inc is a bought right for the 51 ohms reading I got from the sending unit. It got to about 1/4 then dropped back down to 1/8. 
 

if I had to pull the tank I would have definitely cut a hole for access. Cutting it with the tank in place is a little too risky for me. I would be using a hole saw and the pilot drill would hit the tank. 
 

I did find a correct sending unit on eBay sold by Andy B for a very good price but since it’s working I opted not to by it. 

 

Again. Thanks everyone for your help. 

[Plymouthy Adams]

The universal 0-30 sender on their website will not work with the thermostatic two wire gauge.....ohms rating on sender.....30 ohms across 1 and 2 or A and B whichever way it is marked...wiper takes and will split this resistance to ground each leg depending on position of float lever and for good ground......if wiper closer to one leg is 10 ohms the other 20 is on the other leg.  Try and use the single wire sender on a stock two wire thermostatic will result in error readings.  You will have to go forward and pick up a later single wire gauge....then your sender still will not work will be wrong range.   While apples and oranges make fruit drink....no so much in these gauges.   Tanks Inc is thinking the later 50's and up style gauge.....they have never grasped the concept per everything posted by buyer of their products, the thermostatic gauge and how it works.  So unless you sender has two wires for voltage and maybe a third for ground....you are dead in the water.  Again, each end of the resistance unit MUST connect independent of ground and be able to connect to the wires from the gauge.   Read your repair manual, if you do not have a manual perhaps buy one.  Your refusal to accept the fact they sold you the wrong sender is why it has been a year and still not resolved.  IF you wish to use their sender, you will need to buy a gauge to match the operational aspect.  

Edited August 28 by Plymouthy Adams

[Mertz]

Thanks for the input. I know what you are saying is absolutely correct and I may still get the correct sender. The sender I have is a 73-10 ohm. It’s the TAN-ORG unit. They knew exactly how to install it on my gauge with the same instructions as DCM so it has been done before. I told Tanks Inc what gauge I have. The only thing my repair manual has concerning the fuel gauge is on the wiring diagram. 
 

I don’t like the overall result but it is working. If I had easy access to the sender I would change it in a heartbeat.