For OBS / GMT400 owners — pairing a fused relay harness with the 4-Hi mod is one of the cleanest nighttime visibility setups you can run on these trucks. Full writeup with wiring, install steps, testing, and DRL handling: OBS / GMT400 4-Hi Mod: Keep Low Beams On With Highs
Discussion thread for results and methods: OBS / GMT400 4-Hi Headlight Mod — Wiring Methods, Results and Troubleshooting