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.
https://youtu.be/2mQEGTvtnIU
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.