i have a 1989 gmc r3500 with a 454 tbi and i have 4 seprate glass headlights and would like them to come on all when high beams are on and was wondering if its safe to do like in the video because in the comments its says it fries stuff.heres the video

No its not safe. And more than likely illegal.

Without knowing the wiring configuration on the truck, there is no way to know if it will be safe. A relay harness configuration should address those concerns. Fuses/Breakers should keep you out of trouble however, if the proper ratings are used.

A lot of lighting regulations are managed on the state level, so you will need to look up your specific state laws.

The big thing to remember is that the laws are there to protect you, and other drivers. If you do any mods, you are on your own, and do them, and use them with your fellow drivers in mind. If you are driving at oncoming traffic with quad beams, and auxiliary driving lights all running, than you deserve what'* coming to you.

i was planing on making it were if you switch to low beams it would turn off the brights like the video.but i got to thinking you guys are right its going to be to much trouble for the little gain.

Like the guys said, that gauged wire was designed to handle, 20 amps easily....now you are sending 30 amps through that wire, and for safety, the wire thickness might not be enough.......so I wouldn't do it...

No.....not safe.....my granny has a 1990 454 truck with the 4 headlight system......grandpa wired all 4 headlights to come on when the hi beams are selected. The wires eventually corroded (melted near the sockets)......the wires are not meant to handle that much current draw.