I recently replaced my turn signal switch on my 1999 f150 bc it was bad. After replacing it, my left brake/turn signal doesn't work. The running light on that side comes on, just not the blinker or brake. All other lights work, the other brake light comes on and the front blinker work also. Just not that one. It's brand new bulbs and connectors too. Someone help

 

Is the switch new or used? I'd hit the contacts with a contact cleaner first and put a small amount of dielectric grease on them and start there.

 

New switch

 

You say you have new bulbs and connectors in the lights and the left front works fine. Are your connections good in the left rear? Perhaps the connections for brake and signal aren't crimped well enough or they came loose. Since that's your problem area I suggest beginning there by checking your connections.

I replaced all mine recently, bulbs, sockets, hooked up additional rear/turn/brake/reverse lights as well. After 3-4 weeks the reverse stopped working in the main receptacle (the aux. reverse lights were working fine). Upon inspection I noticed the wires had come out.....I hadn't crimped them properly.

After replacing the connectors, re-crimping the wires that hadn't come loose I went ahead and also heat shrinked the connectors (which I should have done in the first place) and everything works fine.

 

it worked for about three weeks but after I changed the switch it stopped working