There is no neg side there is a in and a out the ampmeter just tells You if Your charging by messuring curent draw thru the ampmeter does not mater if it's 6 or 12 volt or if it's neg or poss , most of the time you run the wire from your alt. or reg. to the ampmeter than to the battery and the truck fuses if you hook it up wrong it will not hurt the gauge you will just need to switch the two wires .


Pete