Fuel sender #1

The fuel sender is effectively a float inside the fuel tank. As the fuel level drops, the float by way of an arm, moves the contacts along the rheostat changing the electrical resistance in the coil in the fuel gauge…. thus moving the needle. Or in the case of LGL, not moving the needle.

I’m pretty sure the sender is the original unit (the tank has at some point been replaced) as there’s a British Standard Kite Mark on the top as well as the manufacturers name… “Smiths Motor Accessories Limited”

The needle on LGL has always read “E” for Enough 😉 even with half a tank of fuel. It worked before I started the project so I’m thinking it must be an earthing problem. But this in itself would be odd as there should not be an earth problem with a brand new unpainted galvanised chassis.

Lets see…

2BcNRd+TQPudAhZM%ge3sQ — The fuel tank lives under this cover, held in place by 6 VERY fiddly fixings

Cover panel removed, revealing the fuel tank. The sender is the component with the green wire leading from it. The sticky black stuff around the edge is from the Dynamat. This will get cleaned off before everything is put back together.

Now I have access to the unit, the first thing to do is check the negative contact (green cable) is actually connected properly. Earth (positive) is taken care of by the fact the tank is fixed to the chassis and the 6 screws that fix the sender to the tank, complete the circuit when they mate with the threads in the tank.

I fiddled with the wire a little… and something did happen…

Q1aVrshTQK61YP+21eOBRA — The fuel gauge shot up to “F”… and stuck there.

I disconnected the wire and the needle stayed in place. If there’s no feed, the needle is stuck. A tried and tested tap on the face of the dial and needled dropped back down. On touching off the wire on the negative post again the same thing was repeated.

If I am now getting a reading on the gauge, the contact was obviously bad and if the gauge reads “F” with a better contact, then the sender thinks there’s a full tank… so there must be a fault with the rheostat.

Time to take the sender out…

oXHO7uTbR3SFjgilyxB94w — There is it. The soldered aluminium float is a work of art.

fullsizeoutput_452 — With the top cover of the sender unit removed, the anatomy is revealed

I was unable to get a continuity test between the negative terminal and the rheostat. I was also not able to get a resistance reading. Cleary a fault somewhere.

On closer inspection under a bright light, I found a broken wire…

fullsizeoutput_455 — This thin gauge wire should contact the rheostat but its come adrift so there’s an open circuit, ergo, nothing will happen at the fuel gauge. The wire is so thin, there’s no way I can solder this back together. It’s not impossible but not something I can do.

I assume when I fixed the positive green wire to the terminal during the wiring phase I rotated the terminal and separated the wire from the rheostat.

So a replacement part has been ordered from Craddocks (note the plastic float valve) and should be with me in the next 2 weeks.