Need a hot for roof marker lamps - will this work?

[DeadheadNM]

I’ve got all the pieces I need to install optional GM roof marker lamps in my 99 suburban. For this year, the dash harness connection is supposedly buried deep inside the dash. I’ve not been able to confirm where it’s located.

Therefore I’m contemplating a “plan B” for powering the lamp harness and am wondering if the following idea is reasonable. I’d like to splice the harness hot wire (brown?) with a supply wire at the headlight switch. Seem reasonable if I can identify which wire is hot when the running lights are on?