I don't know what adapter you need for the GPS and would need to know what the current draw is for the unit.
The lightbar Harness I use a 15Amp fuse for approximately 9Amp usage on two 55 watt lights. There is 6 amps more available or you could install a larger fuse. The 14 gauge wiring is good for up to 32 Amps for chassis wiring, and the relay is good up to 30.
The Headlight Harness has a 30 Amp fuse in it already but it runs the headlight AND the lightbar for about 14Amps (assuming 55/60Watt bulb in headlight). Again, half the current load is still available though I wouldn't recommend maxxing it out. I doubt the GPS uses that much though. Why don't you post the power requirement specs and I will take a look. Also what adapter you need. I could make a line off of the harness to connect to a cig lighter/power adapter.