So will it be bad if I use a Posi tap to tap into the license plate light or tail light and use their power instead of doing the whole relay thing? Or even splicing it into the fuze box?
For a GPS, using the typical
box, the current draw is so small that tapping into an existing circuit is no problem.
If your draw will be significant, such as for heated grips or clothing, the best route is some sort of relayed distribution box, like the PC-8 or FuzeBlock. I don't know how much longer FuzeBlocks will be available, as the owner died. FuzeBlocks are neat because they have a relay built in to them.
My preference is always to connect to a factory connection point, but the PosiTap connectors
are pretty good. I had no choice on my BMW but to use them and was satisfied.
Those 'squish and fold' connectors
are something I don't like. I once threatened to tear a U-Haul guy's arm off and beat him to death with it when he tried to use those on my truck. And all the while, there was a complete trailer towing harness right in front of him...