There's a short to ground in the brake light circuit. When you step on the brakes, it diverts all the power in the car to ground, and stops the engine.
If your engine is over heating it could get too hot and quit running, then start again when it gets cooled off. Otherwise, "something" got too hot and quit working, cools off and works again.
it sounds to me like you need to change your alternator ?
there was a recall on the brake light switch you might want to check into that
brake fluid
First off the quit making the 780 in 1990. What do you mean brake relay? Brake light relay/integrity sensor? Need more information
Check the switch on the pedal
There are many reasons why the leveling system will quit working. The first thing to check would be the brake interlock wires, one may have come loose.
Driving a Subaru Outback once (I was borrowing it from a friend), the engine suddenly quit running because it was low on oil. It was a safety mechanism on the car so it wouldn't ruin the engine. I am sure there are plenty of other reasons for it to quit, though.
check your ground wires...they might be loose or detached.
Check bulbs Fuse Stop light switch
No gas.
Brake lights often use a dual-filament bulb. If this gets inserted the wrong way other functions can suffer.