What causes a vehicle's brake lights to behave like this?

when you turn on the head lights, the brake lights are dim as usual, but when you press the brake, one of the lights comepletely turn off even though it was working fine when it was dim. we checked the filaments and they were both intact. we even replaced with a new bulb and no changes. i've also noticed this with other older cars in traffic.



its a 91 previa.



how much to fix? or is it too complicated to fix? also, one of the devices that actually holds the light bulb for the brake is broken because 2 of the 3 wires somehow broke off it. how much do you think that would be to fix?



thanksWhat causes a vehicle's brake lights to behave like this?if 2 of the 3 wires are broken the lamp will not operate at all. If the ground wire is broken the lamp will operate normally lights on, brakes not applied, brakes applied lights off - dim light, and lights on and brakes applied there will be no light. Therefore I suspect you have a ground issue.What causes a vehicle's brake lights to behave like this?i agree ground wire broke