Originally Posted by NoTLaDStyle

The large terminal is the power output - it goes straight to + on the battery.

The small plug has one wire that will show ground - thats the warning light wire. The other wire will show nothing, that wire is voltage sensing, run it to something inside that car that shows +12v when the ignition is on(such as the ignition wire). You can also run it to the battery but the results will not be as good.