Headlight modulators are legal in all states and Canada, as long as they flash at a defined speed. The slower speed of a turn signal relay would be illegal many places. It's good to check the laws before using flashing lights or strobes, because most of them have a narrowly defined set of circumstances under which they can legally be used.

 

Can you draw a simple schematic of how this switch and relay should be wired? I would like to do this modification, but I need instructions.

 

I'd think it all depends on what color those lights are...

 

In Michigan, flashing lights in all the major colors already have specific emergency and precautionary designations, including white. The only exception is the modulating motorcycle headlight which conforms to the official specs, and that includes the requirement that the flashing is automatically disabled at night.