If light is going out you have to believe the electrical is good. It could be coil but usually when it is shorted bad enough to not work it will throw a code and turn on the light. Could be several things. If both sides are locked i wouldnt think its the brake piston seals. They are independant of each other and normally dont go out at the same time. I would lean towards the little spool in the park brake solenoid cartridge. After removing the solenoid coil...the (stem) or cartridge can be removed. It is kinda hard to tear this piece down. It is fine threaded and lock tite'd. There is only a small gap between o-ring grooves to get it unscrewed. It is not necessarily this component...but it is the most likely. Let us know what you find. Good luck.