You need a little more information if you are not going to risk a fire or other problems.
To keep the math simple, lets say each light is 140 watts, running on 14 volts with the alt running.
That equals 10 amps per light.
Most of the small relays used around here are rated at 20 amps, so two lights per relay.
And you need about 10 ga. wire to handle it. You could probably get by with 12, but 10 will have less loss and be happier with handling 20 amps.
NOW, here is where the trouble starts.
If you tie the input of all the relays together, THAT wire will see 60 amps.
10 ga ain't gonna cut it. You will need small battery cable.
8 ga. would handle the current, but you are going to lose voltage and the lights will not be as bright as they should.
I would go with 3 ga.
Or run individual wires to the battery.
If you go with the 3 ga., I would consider buying or building a heavy busbar with connections for the individual relays and one big connection for the 3 ga. wire.
There are several threads here about busbars.
I think this one has some pics.
http://coloradok5.com/forums/showthread.php?t=267400
Its huge, but worth the read.
Also, don't forget, the wire is only half the circuit. The ground has to be able to handle 60 amps too. If all the lights are mounted on one bar, held on with a couple of small bolts, there may not be enough conductor there to handle the current.
Consider another 3 ga wire from the light bar to the neg. side of the battery.
