Code 0703 Brake switch circuit failure; what is it?

My goodness, you even replaced the PCM for this concern? For all that money, you could have had a professional diagnostic test performed and probably even had it repaired. If you have a trouble code, there is a diagnostic routine related to it that should be followed, Guesswork is not really a good diagnostic process, and will result in lots of money spent with no result. Ensure the brake light switch is adjusted properly, then start testing the wiring related to the circuit to find the short that is likely present.

I had my local mechanic look at the issue and he couldn't solve it. He felt the PCM might be bad. It wasn't very expensive.