I made this harness for work. It was actually a fog with high beam mod as the vehicle I did it for kept the low beams with the high beams. It just disabled the fog lights. By law I think this is how it's supposed to be.
We'll be on the open road for a lot on our way to Vegas so I thought it might be nice to be able to use the low beams at the same time as the high.
Normally the low beams go off with the high beams unless you're pulling back on the stalk the whole time. I could modify it to include the fogs but that would get a little more complicated. Basically doubling up on my harness.
It does use diodes and a relay switch. This keep current draw from being too much on the high beams. Also there are diodes to prevent back flow of electricity.