24v systems and gauges?

[SeriesShorty]

Anyone here know much about 24v systems and the gauges/sending units used? Specifically, this is for an ex-MoD FFR.

I can't get the fuel gauge/sender to read and I've already ran out of fuel twice.

1. I've taken the sender out. It was totally gummed up and wouldn't even move. Got it all cleaned and lubed and it moves freely now.

2. The gauge reads slightly below E when off. When I put the key in and turn it to the "on" position the needle will instantly shoot up to level with E. It doesn't read any higher than and as long as the key is "on" it stays exactly at E. Key "off", it drops back down to just below E.

Is the sending unit 24v? If so, I would assume that the gauge is also 24v, as opposed to the civvy models running off the regulator at 10-ish volts.

Thanks for any info you can share...
Jen

[Jeff Aronson]

Jen,

I am not familiar with 24v systems but I have to assume that they're affected by the same electric issues as a 12 v system.

When the sending unit jumps to F and stays there until the key is off, you have to wonder whether the sending unit wiring is working correctly. When you remove the seat cover, you'll find the sending wire unit clipped to the top of the unit, on top of the tank. Turn the key to on and remove the wire - the gauge should fall to E. Clean the spade connector and try the gauge again.

If you remove the sending unit [lots of brass screws] and lift it gently out of the tank, you can turn on the key and move the arm and float with the connection in place. Does that change the indicator on the gauge? If so, then you can surmise that the unit is not sitting right in the tank.

Check the sending unit wire from where it leaves the tank to where it goes to the fuse. Is the wire complete? If you run a separate, temporary wire, does it work now?

Usually, a "F" reading is a problem with the sending unit wire. It could be the gauge itself, but it sounds unlkely in this instance.

Good luck - let us know what you find.

Jeff