I had an issue similar to this a few weeks back. I ended up testing the switches with a multimeter. All switches seemed ok. I ended up disconnecting all if the sensors for about 10 minutes as I manually pushed in (with a large amount of elbow grease) every switch, and flipped the key back and fourth. Then I pulled the dome fuse and left it out for another 5 or 10 minutes. Reconnected everything and still had the problem. So I gave up. About 30 mins later, I was joking with my friends asking if they wanted to buy my Runner so I could sell it and get a Lexus (2001 IS passed by). Got in the car, stared at the light for a few seconds, and watched it flicker and then, FINALLY, after weeks of agony, shut off.
Moral of the story... Threaten to sell your 4runner. It will hear you, and straighten it's act up! lol