I have used relays to control and power a number of things including headlights, fans, heater fans, AC, door solenoids etc. Up to this point I have always wired my relays into the positive circuit. 12 volt power from the source to the relay, then to whatever I am powering up. Then using positive signal from a switch to trigger the relay. Lately I have been seeing wiring diagrams where the relay is in the ground side of the device and often times even triggered via a switch in ground side.

How about some ideas of the plusses and minuses

Pat