Hey Vlad:
If you are considering re-wiring the stock Suzuki harness, I would say good luck! My 1st thought was to just re-wire the stock harness with thicker wire, but when I saw the work that was involved, I would have sold the bike!
There are several quick connects along the length of the harness (wich propably add to the voltage drop. (each conector will add resistance) This combined with what you would have to disasemble, it would be much more work than it's worth.
With this add on harness, you still use the origional switching (this works the relays). You are just really adding a fresh source from the battery. Once it is all installed, all the origional switches work as before. You just have a new power source to the lights.
I just ran the new harness on top of the existing main harness, and to even the trained eye, you would have a hard time noticing this add on.