I had a car that had a failed combination switch (the turn signal, hi-low beam, parking lights switch). I could get the lights to come on if I set the switch to high beam, but not low. A new switch and, viola! Verrry expensive to have dealer repair. If this is your problem, hopefully you have a mechanic friend.
Check the bulbs, check the fuse then check the switch.
If all of the dashboard lights do not work at the same time on a Pontiac Montana, check the instrument panel relay. The relay is located on the firewall in the engine compartment.
Check the fuse, check the bulbs, check the flasher relay, in that order.
check the overhead switch make sure its on if not that you have a blown fuse
Probably the wrong bulbs or the brake lights are getting stuck "on". Or maybe a combination of the two. Check that you have the right bulbs and check to make sure something isn't keeping the brake lights on. FriPilot
2005 Pontiac Montana Fuse Box(es): Your owner's manual is the best place to locate your fuse box(es) and identify your fuses. Don't rule out that your issue is being caused by a bad bulb too - so check fuses and bulbs. See sources and related links below for bulb information.
check for bad switch under dash above pedal arm, generally fail after 75,000 miles
check the connection there was a corrosion in the connection of my firebird that was stoping all of the bulbs to work and check the ground on the bulbs if that don't work i would have to say start tracing the wires under the carpet for bad wires but dielectric grese is the tail lights best freind after you get them working. Good luck
Check the left turn signal bulb. It is probably burnt out.
check your fuses first, then check your bulbs and then your relay.
Check the bulbs Check the flasher
Check the fuse for the tail lights. Also check the bulbs.