Fuel sender woes

[tom'sB2B]

When I bought the car (47 Dodge). The gas gauge constantly read full. I first ran a new wire from the gauge to the fuel sender. That did not fix the problem. 

I then bought a single wire sending unit. I wired it outside the tank to test. No movement when not grounded. When grounded it goes directly to full with no movement in between.

I then bought a two wire unit and got the exact same results.

I'm not sure what my problem is.

Any suggestions would be appreciated

[50mech]

Still running 6v?

[Plymouthy Adams]

47 should be a two wire....you need 6 volts in to the guage….you need two wires to the sender...wire 1 and 2 or A and B however is marked.  These run to the sender a the tank.  The sender then will take each leg to ground simultaneously through the wiper that is the single ground reference at the rear.  The sender reads 1-2 (A-B) approx. 30 ohms....depending on the wiper position this 30 ohms is split by the wiper to ground and if you have 20 ohms on the one leg, there should be 10 ohms on the other leg...this pulls the gauge in both directions and is slow acting also providing a rock steady indication on the needle.  Now as you have hooked it up to other sender, you will have to fully test you system now for possible damage.  Majority of the problems with the older sender is the inside cup and the pivot point that is the wiper contact to the  housing...these get rusted over long periods of sitting with no fuel to protect against corrosion.  This cup and wiper is a hard items to clean for the smooth ground operation of the wiper you are going to have to have to not be erratic. 

[50mech]

https://p15-d24.com/topic/46857-fuel-sending-unit-help/#comment-497406

 

 

[tom'sB2B]

The gauge has two studs on the back. One marked SW (which I assume goes to the switch). The other is marked GA ( which I assume goes to the fuel sending unit. I'm wondering if I have a bad gauge. I will try testing the resistance tomorrow.

[tom'sB2B]

Update. I hooked the new single wire sender up to my other Dodge (1950 truck) and it works. So I guess the gauge in the car is not working. Time to find a replacement for that.

[tom'sB2B]

Update. Changed fuel gauge for an NOS off of eBay. Checked with spare sending unit outside the car. Works great. Test drove it with original sending unit in the tank worked fine and then started bouncing all over the place. Pulled the old unit and replaced with spare. Works great now... finally. Hard to believe both units were faulty.

I also made sure the paper washers on the screws for the gauge.