Fuel Gauge Not Working
The Sheerline fuel gauge was not operating when I purchased "Lady Penelope", so naturally this had to be remedied. Following is the procedure I followed.
This will be the same on the Princess.
Problem: Fuel Gauge not indicating fuel level.
Having previously checked the operation of the gauge itself and confirming it works and checking the wiring and found all to be in order, I decided to remove the Fuel tank sender unit. This is a very straightforward procedure.
Firstly I removed sufficient quantity of fuel from the tank. Then I removed the clevis pin holding the handbrake rods at the pivot point on the diff rear housing and moving the rods aside. Otherwise it would be difficult removing some of the screws retaining the sender to the tank. I disconnected the wire attached to the sender. To remove the 6 screws retaining the sender, I first tried using a stubby screwdriver to remove them. I found it difficult to apply pressure so the screwdriver would not slip from the lot in the screw. So, using my 1/4" ratchet, I fitted a socket and a suitable screwdriver bit. With that I managed to apply pressure to the back of the screw at the same time have the leverage needed to turn the screw with the ratchet. This worked fine. It stands to reason that it is important to clean the slot in the screws before attempting to remove each screw.
Once the screws were removed I gently broke the seal between the sender unit and the tank. The sender unit came out easily. The task was to determine why the sender was not working. The reason was obvious - the float arm was frozen in the empty position (many would say that in these cars the float would spend much of its life close to that position). I removed the inspection plate on the back of the sender unit to see if there was any obstruction preventing the arm from moving. None could be seen. With a few gentle taps on the float arm near the pivot point, with the handle of my screwdriver (taking care not to bend anything), the arm began to move. I added a spray of WD40 and worked the arm through its normal operating arc until it was free. I tested the sender unit using a multimeter set to ohms (the lowest setting possible). The unit works fine. New cork gaskets were made from a sheet then the sender was reassembled and reinstalled in the tank in the reverse order to removal.
I was told by an auto-electrician - that if a wire is broken in the sender unit, I could undo a few winding and re-solder. The few windings would not significantly alter the accuracy (which is often questionable).