ammeter gauge

how do u intall this on a 91 vw passat

The meter would be wired in line ( Series ) to either alternator, or the battery. Proper polarity of the installation wiring is paramount, as doing so backwards would cause the needles armature to deflect past it's spring rate. You will have to ensure that the correct wire guage is also used in the installation. That will be determined by the maximum current output stated by the alternator manufactor, or vehicle maker. You will also have to use a grommet, and protective teflon or similar tubing to protect the cable(s) against schaffing. it would be alot easier and easier to use a voltage guage. The fact that you have live fluctuating current running within the cabin area, is somthing you must be sure about. Regards EVIL Teken . . .