Using a relay might make your lamps brighter by doing two things.
1. The current to your lights must run thru your light switch and all the wire from the source to the lamps as it is now wired. All that adds resistance thus reducing the current to the lamps.
2. Using the relay and using larger wires connected close to the power source allows for even more current to reach the lights. An added plus is less stress(load)on the light switch means longer life.


Six volt guy living in a twelve volt world