well if your truck had power window it would have another heavy load on that circuit which is why those things are on there own run circuit. it is always a good idea to find out how someone might have wire something so that you know where to look if something quit working again.
this might help you understand things. run & start and run & acc are powered by the red wire and the run only things are powered by the pink wire

 

Cool diagram, the one in question is black with a red (pinkish) stripe. I don't have power windows, but that too is on the same circuit even though it has no fuse in it because I have manual everything.

 

the diagram is pretty universal to all trucks. the fuse panel is pretty much the exact same between 81 and 93 and it was may the same whether you had manual everything or power everything. if you got the parts to install power window you could wire it to the fuse panel.

 

What I need or want to do next similar to that is install power locks and trip them with a remote and alarm. I have (somewhere!) a few powerful lock actuators I got back when i did a lot of car audio and systems. I need to find out if an alarm I would buy is able to trip aftermarket lock actuators on both lock and unlock functions. Normally the alarm only hits the existing lock system with a pulse of 12vdc and the system wags between lock and unlock.