Fuel tanks

[fig]

Hi
There is not a live + on the sender. The live is via the ign switch and the fuse to the one side of the gauge. the other side of the gauge goes to the sender. the whole thing is very simple it works like a string of sausages with the sender sausage providing the vairable restance required to operate the gauge full scale. DONT CONNECT A LIVE TO THE SENDER - can you imagine that fiddly resistor glowing red hot inside the gassy confines of the tank before it pops and sheds a few sparks !!! -- sounds scary to me!
Cheers
Bill

surely in the string of sausages it doesnt matter what the order is, there is still curent across the sender?

Yes. You don't want to apply direct current across the gauge, but the sender is designed to take the current; it's just a variable resistor. Resistors are designed to heat up. I may be wrong, but I think the sender is designed to be cooled by the fuel.

The gauge is essentially an ammeter that reads the changing current as determined by the variable resistor in the sender. You always connect an ammeter in line with a resistor or risk damage to the ammeter.

[forcecooled]

Yes
there certainly is potential at the sender connection. Remember, that there is minimal current there as it has already has passed thru a resistance ( the gauge), so its not as though you would be connecting a live lead from the batt+ terminal directly to the sender unit terminal, which would dead short the sender , burn it out and render it useless, and possibly create a dangerous situation.
Cheers
Bill