[mightycarlo10]

I have a 1987 Monte Carlo adn I'm having an issue with the brake lights. When you turn the headlights on, the brake lights come on except for the third brake light. When you push the brake with the lights on, the third brake light comes on. So the two taillight brake lights are always on. Also, if the headlights are not on, when you push the brake, the parking lights come on. Any ideas on this problem?

[NEW INTERIORS]

Check all the grounds,They will make things go crazy.

[grandpaws 57]

check bulbs to see if one filliment is touching another.Did this start all of a sudden?Problems in past?

[speedydeedy]

Are you using LED tail light bulbs?

[mightycarlo10]

It didnt do it when i bought it, but I was missing a bunch of bulbs so i replaced them. Could this be because of a wrong bulb?

[vettedreams2001]

IMO I would check the bulbs to see if they have the correct number of filaments and then go from there.

[cucumber1949]

Also, I have seen where a dual filament bulb (parking and brake light in one bulb) can be inserted 180 degrees out of phase in the socket. This will cause brake lights to come on when the parking lights / headlamps are on, and cause the parking lamps to come on when the brake pedal circuit is activated. If you have recently replaced the bulbs, you might want to take the bulbs out and turn them half a turn before inserting to see if that may be the issue.