Basicly I'm trying to wire up four 100 watt lights on my roof im planning on running my power from the battery with a fusible link then thru a switch thats good for 430 watts, then grounding the lights on one of the screws on the roof rack mounting rail, I'm just wondering if 10 gauge wire would be thick enough to handle a 400 watt load if not how thick would i need to go?
To put it as best I can... Not, Stop!
The 400 watts of lights will require 30+ amps to operate at the best light output and 10 ga wire, IMHO, is rated for just the 30 amps plus a safety factor.
The best approach is to setup the lights in pairs, running two fused 12 ga power wires, to two separate relays. The relays can be actuated with one switch on the dash but two circuits after the switch.
The ground wire(s), here is where there are a lot of different opinions. First the roof rack mounting hardware is not a good grounding point. Second even if the lights grounded through the hardware there is no guarantee that this path will maintain a good flow of electricity over time and support the current flow needed for the lights.
Run a good ground back to the battery and maintain the same gauge wire(s) as the power.
PLEASE NOTE: It is important to use relays and gauge the fuses, wire and relays according to the draw of the circuit for safety reasons.
Fact being - I do not think you want to see your vehicle go up in flames in the middle of a night run.
One more thing, 30 amps running through one switch with wiring running inside of the vehicle is just plain crazy even if the sw can handle 30+ amps.
using relays and a fused power wire can eliminate the possibility of a fire and possible accident.
Luck to ya, ltr,
