I have a 94 850 and with the lights on the turn signal works until I press the breaks then they stop working. When I let go of the brake they start working. Also They will work fine and have no trouble in the daytime with the lights off.....Any suggestions.....most of the time they dont work with the lights on but occasionally they will work.

Thanks
K

 

Check the ground for the tail lights! It might be one side mine was fine until I put the parking lights on with the brakes on with the turn signal! Mine was only when the left turn signal was on! The left ground wiring at the socket was loose. Fixed it and they all work ok now!

 

I think you have a problem with your light switch. Pull it out and see if it's falling apart.

 

If the problem only happens when you step on the brakes there is a good chance you might have corrosion back at the bulbs in the rear. That or a bad connection or broken circuit in the plastic. That is about the only place the brake light circuit physically gets near the running light circuit. You should also check for a good ground back there as it might be back feeding the circuit by using your turn signal circuit for a ground when the brake switch closes.