Join Date: Dec 2004
Location: NorCal, south-bay.
You could use a single-pole double-throw if that what you get a deal on. You just need to figure out which are the normally open and normally closed connections (use a cheap multimeter, you will want it if you have problems later). You will want to use the normally open terminals.
I would take a wire from your dash or side lights, through your switch, through the relay coil, and to the low side of your headlight low-beams (red-green on a '99). As has been mentioned, these headlights are switched on the low side of the bulbs.