Originally Posted by phattyduck

Step 1: Do you have a trailer light converter installed? If so, unplug it for now. Most will be plug-n-play and easy to remove/re-install once the panels in the back are pried open.

Step 2: Return all easy to change bulbs back to halogen

Step 3: Have a helper try all different combination of lights (brakes, turn signals, parking lights, and gear positions) while you watch from outside/rear of truck.

Report back your findings... Oh, and what year/trim is your 4Runner?

Have you noticed any odd behavior of your dash gear indicators?

You may have a problem with your gauge cluster flex circuit board... I had to replace mine a few years back. At the time, I still had all stock exterior bulbs and was getting some similar issues to what you are seeing.

-Charlie