[Gunter]

Slantnose: You are asking some very basic questions; it's alright not to have any mechanical/electrical knowledge; it's a vast field.
I think what nine9six means is that you should not expect that other members on this board do the research for you, like parts numbers etc.
Get a Bentley, read, read.......
Learn how your multimeter works, read the instructions for it.
To give you "Electricity 101" on this post is too much to ask.
Yes, this board is extremely helpful but you need to do some ground-work. Get some books, learn the basics on how to use your meter;
It is either the sender, wires, or gauge; a simple problem.
There is even a electrical schematic in the Tech Section on PP.

I remember a post not too long ago where it took six pages to help someone with a fan belt issue. LOL.
Best wishes.