are the seat belts in an 87' ram supposed to lock up when you slam on the brakes?

Probably, they're hooked up to an inertia switch. When you come to a sudden stop, the switch will lock the retractor so you don't hit the dash or go through the windshield.

thanks how do i check to make sure the switch works?

Well do your seatbelts lock up or not?

well i don't wanna slam on my brakes and hit my head on the steering wheel if it doesn't work

You'll know; it will take up the slack in less than 4 or 5 ". Just hit the brakes from about 20mph and let your body lean forward.

ok thanks