I have a 2004 f150. I am having a tail light issue on the drivers side. All running lights work. (Including drivers side) when I turn on my hazards all lights work. My blinkers work but it blinks really fast on the drivers side. When my truck is in park and I press the brake peddle both brakes work. But when my truck is in drive the drivers side brake light does not turn on. If my running lights are on my drives side brake light will turn off when the peddle is pushed. This only happens when the truck is in drive, the brake will turn on while in park. I have replaced the bulb and I am still having the same issue. What could the issue be?

 

The rapid blinking is simulating a burnt out stop / turn element in the bulb.

This could be a few things, but the 2 things that come to top of mind are :

1. Bad ground to the driver's side bulb socket.
- This is hard to diagnose looking at the bulb, as it would be a slightly dim look to the bulb.
It could be in the bulb socket itself, or where the wire is grounded to the frame under the truck ( G110 ).
Check from the ground in the bulb socket to a known good ground for resistance.

2. Dirt and/or corrosion in the trailer tow adapter.
Check both the front and the rear of the trailer tow adapters. The 7 pin can get "gunk" pressed into it from the back of the plug ( facing the front of the truck ).
You can do a quick test ( not complete ) by pulling the trailer tow adapter stop / turn fuses ( 36 & 42 - verify the fuse location with your MY, this is 2006 location ).

 

My trailer hook-up was cut off, now my left side turn light and brake light don't work, what can I do. Fuses, bulbs, and MSF seem fine.