Weird Fuel Gauge Problem after installing new harness

[Chris in MA]

Hi,
I replaced the wiring in my 40 with new from Bauer, Cowl/Engine and Headlight harnesses.

Everything came out great and is working as expected, with the exception of the fuel gauge.
When idling, it reads accurately. When driving, it shows as empty. On the old wiring, the gauge would read between 1/4 -3/4 when driving (3/4 being the full reading, 1/4 being on the empty side. The needle easily went from E to F, so it was not stuck. The wires are in the correct places on the gauges according the the diagram.

Any thoughts on the fuel gauge oddity?

Thanks.

[rotorwrench]

I'm not sure if your harness included the wire from the indicator back to the sending unit. The power circuit from switch to indicator should be in that harness you indicated. If it has an original King Seeley sender is also an unknown. A lot of folks use a new tank due to corrosion with a modern replacement Ohm controlled sender unit so it can make a difference.

[JayChicago]

A maybe:
Gauge going to empty when driving could indicate intermittent open circuit to the tank sender. You were making your front harness connections in the turtle cover on the firewall. Also in there is the connection to the sender wire (solid yellow) in the rear harness. Check for loose connection there.

[Chris in MA]

Thanks. I am going to guess it's the original sender. I have had the car for 20 years, and it has been in my family for 30 years before that. Yes, that leaves 30+ years of an unknown. The tank appears original as well. Will check the wires against the diagram.

[19Fordy]

Remove our gas tank sending unit and see if the float is leaking and full of gas.
Also, move the sending unit arm thru its arc of travel to see what readings you get on the gauge. To do this you have to ground the body of the sending unit to a good ground like the trunk floor latch.

[47topless]

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You need to polarize your voltage regulator.

[JayChicago]

Guys, from the original post:
“When idling, it reads accurately. When driving, it shows as empty”

[rotorwrench]

It will never hurt to flash the field on a generator but they don't lose the residual magnetic gauss from the field pole shoes quickly. I only do it if the generator has set a long time, it's being replaced with another unit, or there was an issue with the regulator function.

There may be a loose terminal or intermittent wire connection in either the power side or the ground side of the indicator system. I have home made long jumper clip wires that I can install for testing to narrow down where the problem is in the circuit.

[Chris in MA]

Hey all, Just an update. I checked all connections; the solid yellow was not fully connected. I had to expand the size of the barrel connector, and all is well. I will point out that while the battery was disconnected, I managed not to have a spark after putting it all back together. No power from coil. Chased that down to a coil failure. This was a new coil from Carpenter about a year (maybe two) old. The previous coils were from Skip and lasted about 10 years each. Need to send those two back to Skip...

[hueyhoolihan]

Originally Posted by Chris in MA

Hey all, Just an update. I checked all connections; the solid yellow was not fully connected. I had to expand the size of the barrel connector, and all is well. I will point out that while the battery was disconnected, I managed not to have a spark after putting it all back together. No power from coil. Chased that down to a coil failure. This was a new coil from Carpenter about a year (maybe two) old. The previous coils were from Skip and lasted about 10 years each. Need to send those two back to Skip...

i'm curious as to what type of coil was defective. a canister or an integrated one used on a diver's helmet distributor?

[Chris in MA]

Original style for a helmet. 2 screws.