I have noticed a weird problem

The headlights and everything work fine. But when I park the truck I will first turn the headlights off, and shut the truck down. Then immediatly after shutting down, the headlights quickly go bright and then dim out until off. Only takes a second.

Any ideas what this could be?

I know I might have a bad ground somewhere (most likely batt terminals I think) Was gonna wait till its a nicer day to tackle those. Never seen a vehicles light brighten and then dim after shut down.