i wiring up my 4 hella lights on the roof i think i read u could use a cat 5 cable i just dont want 2 use 4 diff wires on each light an twist them all the way down so could i do the cat 5 cable ??

 

Do a search and you'll find a wealth of info, but to answer you question...I'd use at min., a 10ga exterior rated stranded wire and wire the lights in parallel. I like using marine grade boat wire, its oil, gas, and UV resistant and stays flexible when cold and willn't harden like pvc jacketed wires. Cat-5 is 24ga and if you use that it'll just flash your lights on before burning the wire in half, just like a fusible link

http://www.engineeringtoolbox.com/am...uge-d_730.html

Shortest run on the chart is 15' but it gives you an idea about voltage drop. A 100W light pulls almost 9 amps at 12V...think bigger wire..