Ford is the world's leader at hanging unnecessary computer modules onto every conceivable system that never needed one before, and this is one more. You did notlist a model or an engine size to help me find the right wiring diagram, but I looked at something that should be close. I used one for a 150 with a 3.5L engine.
Th turn signal switch is a computer module, so it will always be a good suspect when there's a problem related to it. It sends a digital signal to the body computer which turns on the signal lights. That means you cannot use quick and simple voltage measurements to diagnose the cause of the problem. A mechanic will need a scanner that can access the body computer to see if it is seeing the command from the signal switch. In this case the brake light switch is a separate input to the body computer. With two dead functions, it is not likely there are two different defects at the same time. That makes the body computer the best suspect.
It is likely a new body computer will have to come through the dealer's parts department, and the service department will have to program it to your vehicle. They should diagnose this properly before spending your money on parts though. My diagnosis is based on logic and probability, which has a good chance of being wrong.
Saturday, May 20th, 2017 AT 9:40 PM