Will these plug directly into my existing wiring harness?

Yes — these mount at factory fog light locations and use OEM connector fitment. Your truck's original wiring harness connects without adapters or splicing.

Do I need to replace any wiring or add a relay?

The stock electrical system supports these units. No relay modification or rewiring required — pull the old units and bolt these in place.

What's the brightness difference compared to the halogen originals?

LED output is noticeably brighter and whiter — you'll see better penetration in fog and rain. Power draw is also lower, which reduces load on your alternator.