69 Fuel Gauge

[UKD100Sweptline]

I feel like i'm missing something simple, so any tips appreciated. Only owned the truck about 3 months.

When i bought the truck i knew the fuel gauge was broken and the previous owner had even brought a new sender unit to fit, but never got around to fitting it

So the fuel gauge has never worked, but all other gauges work fine (temp and ammeter). Fuel gauge permanently reads below empty.

Test 1
First thing i found was that the original sender unit wasn't connected either end, so wouldn't have worked anyway. So to double check i ran a fresh wire between the post on the sender unit and the post on the back of the gauge, and with ignition on, still reads below empty. (in my mind that means the sender unit is faulty)

Test 2
I checked the voltage on the live terminal supplying the gauge and got 12v

Test 3
Next test was the gauge, so leaving the new cable attached to the post on the back of the gauge, i grounded the other end on the body of the truck, and with the ignition on, the fuel gauge needle went to beyond full. (in my mind that means the gauge is OK??)

So today i removed the old sender unit and fitted the new one, however when i repeat test 1 , 2 and 3 but with the new sender unit fitted i get the same results. Tank is three-quarters full but gauge still reads below empty.

Anything else i can try??? or any ideas if my assumptions above are wrong??

Thanks

Jon

[PwrWgnDrvr]

Are u sure the float is actually floating?

[TheMopars]

How's corrosion/rust where the new sending unit attaches on the tank? I had a similar problem. I'd bought a tested used sender
but it was a bit rusty there as was my lock ring. I removed them all and cleaned them up with a wire wheel on my drill down to
clean bare metal and it finally all worked.

[UKD100Sweptline]

Thanks Guys, more things to check.....

[UKD100Sweptline]

Are u sure the float is actually floating?

Yep got back in there today and can see the float is floating and the arm moving

[UKD100Sweptline]

How's corrosion/rust where the new sending unit attaches on the tank? I had a similar problem. I'd bought a tested used sender
but it was a bit rusty there as was my lock ring. I removed them all and cleaned them up with a wire wheel on my drill down to
clean bare metal and it finally all worked.

Its a new sender unit, lock ring is bare metal. Have even tried grounding the tabs on the lock ring of the sender unit using a separate wire whilst the sender unit connector is wired to the post on the back of the gauge. still no movement on the needle. when you move the sender unit arm you can feel the everso slight resistance which is hard to describe but what id expect, a bit like running your nail along a comb

Only way i can get the needle to move on the gauge is to ground the post on the back of the gauge to the body of the truck. head scratching....