I know they shouldn't have anything to do with each other, but try disconnecting the headlight modulator and see if it makes a difference. Just something to try.
On a side note, I know a local that has this and his signals are not led, there was something that he had to take off, a jumper or something like that, if not it would act weird and then the fuse would pop. It has to do with LED bulbs, helps it so they don't flash fast, I can find out what it was if you can't find anything else on it.
IF YOU ARE GOING TO BE DUMB, YOU BETTER BE TOUGH! 2003 1800C BLACK & DARKSIDE!