I have 2 155 Watt KC daylighters up top. I used a 4 wire trailer wiring harness but I split the current between two wires each (+ & -). That way instead of about 25 Amps through a 18G wire I get about 12 Amps through it and the 18G works fine. Since you have 4 lights, a single harness may still not be enough. You might consider using 2 harnesses. Maybe one for the Positive side and one for the negative side.

The harnesses mentioned above look impressive but I don't know how well they will hold up outside, on the roof. For the ones like Pnut used try checking at an alternator supply house. That's the route I would have tried, but I already had my setup when I thought about that.