1974 cabover brake light switch location??

[Colomack 6]

New to the forum but have used the knowledge on here for a long time. I recently got a 1974 f model cabover and I can't get the brake lights to work but if I supply power to the wire off the turn signal switch that goes to the brakes I have lights, so I bet it's the brake light switch, but I can't find it! Any ideas? 

[75T 37]

It might be in the panel where the brake valves are. 

[Colomack 6]

Under the cab on the driver's side?

[Hobert62 1,226]

My B model had it on the tractor protection valve behind the cab where the trailer airlines started from.   

[Colomack 6]

Thanks for the replies, I found it under the cab above the driver's side tire under a plate attached to the foot treadle valve. I am new to the older Mack's and was wandering if there is any way to get a wiring diagram for these things? Lots of fingers have been in the dash before me and it's a spaghetti mess, I need to know what it was supposed to be like so I can start sorting  it out