Ok I have a 2011 F150 5.0 fx4, my trouble starts with the fast blinker and no brake light on the right rear only. Things I have tried are, checked all applicable fuses/relays, changed both bulbs (twice) changed bulb receptacle from left to right so those are good, checked multifunction switch and cable harnesses for loose wires, ended up changing the multifunction switch because im running out of options. Problem still persists.

 

Ok I have a 2011 F150 5.0 fx4, my trouble starts with the fast blinker and no brake light on the right rear only. Things I have tried are, checked all applicable fuses/relays, changed both bulbs (twice) changed bulb receptacle from left to right so those are good, checked multifunction switch and cable harnesses for loose wires, ended up changing the multifunction switch because im running out of options. Problem still persists.

 

The MFS cannot cause this symptom on a 2011 since the brake/turn signal doesn't go through the switch.

There isn't much more a DIYer can do without the diagrams.

Can you tell if the relay for the RT lamp for the trailer in the Battery Junction Box works when the right turn signal is on? If it does, you probably have a wiring fault. If not, it's probably the Body Control Module.

 

Need to check the power at the bulb receptacle when you press on brake pedal. Check front one too. So you have left side working just fine?? Double check the kinda bulb that goes in there.

 

haven't been able to check the power yet but, I took both receptacles from left side and moved the right side over to left so its not a bad receptacle and same with bulbs. left side works fine, front right works fine, no brake or signal on right rear only...

 

I had fast flashers on both turn signals at once. This happened after right side went bad. I changed front and back flashers. Then both sides flashed fast. During oil change ford said they replaced 3 bulbs and flashers now work..

 

Test the light socket, make sure everything in it works , including a good ground in the plug, if not, check the plug that connects the lighting wiring harms to the rear of the truck.
Should be somewhere between the cab and the bed of the truck.

 

Two threads have been merged. One thread per subject please, as it causes a lot of confusion for those trying to help.

 

I had a similiar problem on my old car and it was the ground. I found this by grounding the receptacle with a jumper cable attached to the frame. Flashed beautifully grounded to the frame.