I'm trying to understand what the differance in senders are ...? ....Whats the skinny on identifying VDO senders switches..? What do the markings on them tell you ..? How do you read them...? and also where does the idiot light and gauge hook up on the sender (G and Wk)...?...I was told "G" is for the gauge and "wk " is the idiot light ..?..is this correct..?......