The rear light socket plate may fail causing a brake light or other rear light to stop working.Google+
Car Problem Reports
Pontiac Montana Rear Lights May Not Work Due to Rear Light Socket Plate Failure
Pontiac Montana Problem
Average Mileage: 92,750 mi (60,000 mi - 135,000 mi)
brakes light failed, replaced with new bulbs, not working, noticed that wire pins in plate were a little flat and not making good contact, carefully bent wire contacts up a bit, it worked, old bulbs were fine, cost $0.00, tools: small screw driver or paper clip, time to fix: a few minutes
Visitor, 2000 Pontiac Montana
Determined it was the black wire causing the short, made a direct connection with a wire I fastened onto the plate and connected it to the lead black input wire bypassing the harness connection. Had the exact same issue on a 99 Montana Driver's side brake light.
Visitor, 2004 Pontiac Montana, 90,000 mi
Right rear brake lights fail. Entire socket assembly and bulbs have been replaced. Bulbs always have a melted and scorched end. Now the left side does not work although all the bulbs are working...brake lights do not. Only the brake bar at the top rear window works.
Visitor, 2000 Pontiac Montana, 86,000 mi
Brake lights burned out repeated, almost as soon as they were installed, then stopped working altogether, some melting and corrrosion in sockets. All other rear lights fine. Replaced rear light circuit boards ( about $25 each) and new pigtail harnesses (about 50$). Problem solved, for now
Visitor, 2003 Pontiac Montana, 60,000 mi
looks like previous owner applied some Vaseline to the socket, replaced after finding out light was not working. did not light up until I put some pressure on the bulb, then it worked for about 10 miles. the next trip I noticed it was out again. after that trip I noticed the area where the break light was not working seemed warm to the touch. this makes me think there is some shorting going on.