I have a Blazer S10 from 1988 and I think I have a problem with the central locking of the doors.

When I open the car with my key ( both driver and passenger's side ) only that particular door opens. But I also have those electrical buttons on the inside and both doors open or close when pushed so I do have central locking I think ?... where should I start looking to fix this or is it normal behavior ?

 

Nothing is broken, So nothing needs to be fixed. You have power locks. But putting the key in to unlock either passenger or driver door wont unlock the other door as well.

 

So i have to open up the door and afterwards push the button to let a passenger in ... really, who came up with this ?

 

Yup, you own a 1988 blazer, cant expect too much out of it.
only other way around would be installing a keyless entry system.

 

Yep, actually what you mean is, "Who DIDN'T come up with this?" Haha

I had an 84 S10 Pickup and it had nothing, no power steering, no power brakes, no vents on the dash even, only thing that it had on the "Optional Equipment" list was the Dome Light. Pretty lame....

 

Still lucky then I guess, I do have powersteering and powerbrakes, AC, electric windows and a button on the dash that unlocks the rear window.

Keyless entry, I like the sound of that. Must investigate.

 

I was lucky that my 93 Jimmy came factory with keyless entry.

 

Heck, my blazer doesn't even have a lock cylinder in the passenger door. I couldn't open the door for my wife if I wanted to, if it's locked!

I doubt it came that way, so somewhere along the line it must have broken, and been removed? I have no idea.