Brake lights on a 81 GMC

[Roper]

All lights/signals work on my truck except fot the brake lights.Also the brake lights on my trailer dont work now either. Truck is a 81 GMC. All fuses seem to be working on the fuse box although there are circut breakers there that I didnt check. Have no idea when the brake lights stopped working.
Have not checked the bulbs because I cant see all the bulbs being blown at the same time.
Backup lights work to.
How do brake lights work? On the brake pedal I cant find any electrical conections that would engage them. Cant find any fuse marked brake lights.
On my 87 when you press the brake pedal it moves away fom two electrical connections(breaks the circut?) but on my 81 there are no connections. There is the bracket there for two connections(switches) but no wires or switches like on my other truck?
Here is the thing though. I have had this truck forever. I used to have brake lights.Well im pretty sure I had brake lights. I must have had brake lights. Yes im sure I did.Anyway I didnt remove the switches or wiring so they must not have ever been there? Right? Im totally confused. So do the break lights work differently on a 87 than they do on an 81?
Any ideas about how I could fix them? Thanks
PS
Man I looked everything over and that truck must have been without brake lights since I had it. The factory switches that disconect when you press the brake pedal are gone, a long with all the wireing.
So I guess my question is now how do I wire up brake lights from scratch? Example I need two of those switches for the brake linkage but then where do I hook the wires to?
Its winter here in Alberta. Im working outside. The wireing is different on the 87compared to the 81 and I dont want to tear the 87 a part to try to figgure out how to wire the 81 if I can help it.