I am surprised no one has yet mentioned checking and upgrading your standard wiring to give a closer to 12 volt output at the light
by the time the voltage drops through the system from battery to switch and back to lights you are lucky to be hitting the bulb with 9 - 10 volts, re-wire the set up with additional relays and voila closer tyo 12 volt at the light less load on your swicth and wiring and MUCH brighter lights with NO CHANGES to visual stock look (except a couple of well hidden relays)
Daniel Stern did a great write up on this here..........
Daniel Stern Lighting Consultancy and Supply
maybe that helps maybe not??
M@