Would I be right in thinking that each light on full beam will pull around 4.5A?? Therefore a cable rated at 16.5A would be happy running both headlights??

A general rule is that any fuse or wire should not be loaded constantly to more than 80% of it's design capacity. Therefore 60 watt main beam light at 12 volts is drawing 5 amps.

The theory is
5amps * 100/80 equals 6.25
next fuse up is 7.5 amps times 2 is 15 amps. 80% of your cable rated at 16.5 amps is 13.2 amps.

Theoretically it's wrong but in real life It'll be fine with a 15 amp fuse in the line as voltage drops over the short length of a seven is minimal.

Happy days!

Thanks for that!

A 1.0mm thinwall cable will be perfectly ok running both headlamps (55W each so roughly 9.1A) Interestingly I found that my 10A headlamp fuse was running hot enough to melt the plastic fusebox housing while not actually blowing the fuse. Uprating to 15A solved the problem (and the burning smell)

Wouldve used a 15A fuse anyway cause thats what was in the bike loom for the headlight. Seems a bit heavy for one bulb I thought but hey! Suzuki must now what their doing!!!

Thanks for the advice guys.