I have a 2000 Explorer XLT with 200,000 miles on it. Runs perfect, doesn't leak a drop. Life is good. Problem is, recently when I put the vehocle in gear, after taking my foot off the brake, the doors don't automatically lock. Doesn't happen every time, just some of the time. The door ajar light on the dash will light up. Once, when I manually locked all of the doors, the ajar light went off. Now it stays on and also the interior light stays on after I exit the vehicle, then extinguishes itself after it times out. Needless to say, all the doors, the rear hatch and the rear window are securely closed. Any ideas on what the problem could be would be appreciated.