Hello Andy, it's a similar principle as spot light wiring, just you use the power lead from the switch to turn the relay on, I suppose you could use 2 relays, one to run the main beam on both sides, and the other to run the high beam on both sides, it will be worth while using heavy duty wiring on both of these as well.
There are a few threads on this forum regarding the wiring of spot lights, just swap either the live feed on the diagrams (or switched power) and bob's your uncle. Paddocks do relay kit's for abour £5, either buy 2 of these or just buy the relays and cabling.
Best of luck matey