I have a 1978 K5 Blazer and the rear door lock didnt come with a key when I got the truck, does anyone have a diagram or know how I can disassemble the tailgate the right way to replace the lock?

Thanks

 

The removal procedure is the same for the power window and the manual window. You have to open up the tailgate and position the window so that you can see the bolts for the outside chrome piece. There will be holes through the regulator that line up giving you access to the retaining nuts with a socket and some extensions. If you do this with the tailgate down, you'll want to support the window on something if it is out 1/3 of the way or more.

LMCTruck.com's catalog has a bit of an exploded view showing you want they offer inside the tailgate.

This lock should use the same key as the rest of the doors. You can often get a locksmith to re-key the lock to match your door key.