No brake lights after new B.L. switch and new Ma.Cy.

[sheetshaker]

I was hooking up a flat 4 trailer light plug when I noticed I had opposite operation of my brake lights. Always on except when I press the brakes. When I press the brakes the brake lights go off. SO I changes the brake light swith and the brake light didn't come on at all any time except when the hazzards are on.(they share the same bulb.)
I also changed the master cylinder about a month ago and something could of happend then as I never checked for brake lights and only bled the front wheels.
I had a guy bleed 'em. And i don't think he did it right.
Thanks for any help as I need this thing to run in oreder to get get me New Orleans for hurricane Volenteering.
Mike

[JaVeRo]

Do your turn signals work correctly?

Was the trailer still plugged in when you checking the problem?

Did you check it without the trailer?

The reason I ask is this, If a trailer is plugged in but doesn't have good ground then the tail light to the trailer can backfeed from the ground side of the trailer bulb back thru the brake light circuit and thru the truck brake light to a good ground.

It doesn't sound quite like your problem but anytime the rear lights start doing something wierd I check the ground first. Use a circuit tester and see if the voltage going to the bulb matches the way the bulb is behaving.

Check your brake lights and turn signals with the tail lights off, then check them again with the tail lights on. If it acts different then chances are it is the ground. If you are getting voltage but no lights then its the ground. If the behavior changes when you plug the trailer in then it could still be the ground but now it's grounding through the trailer.

James

[strmn94]

was the brake switch replaced?
or did the mechanic open it up and clean it?
there are 3 sets of contacts, so it is like 3 switches in one. if the connector was put on wrong, that would cause the backward operation of the brakelights.