Bob, did the mechanic/helper check for 12V power at the "K25 Relay" (note that it may be a different # relay,so confirm by looking at the relay location diagram on the bay door) when the brake pedal is depressed? That is an easy place to get to to start the troubleshooting.
If you have power at the K25 relay (the terminal 85) then you know the power is getting through the brake light switch.
For troubleshooting, you want to split the circuit your testing into sections (so split to half before the relay, and the half after the relay to the lights). Now if you have power at the relay terminal 85 you know everything from the battery, through the brake light switch to that relay is good. Then you would know the problem is from the relay to the brake lights (and don't forget to check the relay it self). If no power is at terminal 85 then you make your next check for power at the brake light switch. or connector C6-16 (if you find it).
At least that's the way I would proceed.