I have a 99 F150 4.2L
Just changed brake master and front pass. side cal and now my brake light is on and wont go off! tryed playing with the parking brake and nothing. I seen a code a few weeks back something about a ground short in brake? but brake light on the dash never was on until I replaced the cal and master cel. any idea's???

 

Did you mess with the float switch in the brake fluid reservoir? Did you hook it back up? Did you fill the reservoir and verify float switch operation?

 

What was the exact code number?

 

Sounds to me like a problem with your Fluid Level Indicator (FLI) switch in the reservoir. Either you didn't hook it back up when you swapped MCs or you have a bad one.

Do you still have the old MC? You could try swapping FLIs if it is indeed hooked up and just not working.

 

it was the new master unit. I put the old unit back on and light went out.