Working on a 2012 Bluebird bus with air brakes. The problem we are having and currently working on is that the stop lights work BUT........ with light pedal pressure (enough to turn stop lights on) the relay will de-activate after about 10 seconds. If you press the pedal on a little farther the lights will come back on and stay on all day if you wanted. We had a spare bus and we pulled the switches out of it after the first bit of testing led us to the switches, and we swapped these for the ones we thought were bad. Problem is exactly the same lights go on, stay on for about 10 seconds and the relay clicks off and lights go off, press harder and they come back on just fine.
Tomorrow we are going to do some more testing on the control side of the relay to try and verify if the body module is bad or if we are losing power at another place. From the wiring schematics the relay is grounded off the body and control is off the BCM. Power on pin 30 comes from the switches ( there are two on the inside of the firewall) and 87 goes out to the side panel and to the back. The draw from the rear lights is only 4.8 amps.
Will update tomorrow after we poke at it some more.