I have an old 1988 F150 and I wonder if and when the seat belts should block.
Both (main) 3-point seatbelts (drivers side & passengers side) retrackt reasonable, but they dont lock/block when pulled fastly.

It might be a dumb question, but since they both dont work, I wonder if they are just both broken, or it is some other (electrical??) mechanism?? There is some wire on both sides...

 

That's the work they worked when new. I just went and checked my 89' Bronco that I bought new and they were the same. They have always worked that way.
I beleive that a weight shifts during a sudden stop locking the belt. Kinda hard to test without a telephone pole.

The wire is to tell truck you have your belt fastened.

 

I found somewhere else indeed that there is an inertia switch, which locks the belts when the car makes a sudden stop.

I tested it by braking rather firmly, and indeed the belt locks (at least the drivers side!)

 

Yup, your right on the electric lock. Pretty sure both sids should.

Adrianspeeder

 

They use a mechanical pendulum - nothing electrical. It will lock the reels during an impact, or when the body is severely tilted.

 

Hmmm, swore they were electric, but steve has spoken. Welcome to F150online.

Adrianspeeder