are you getting fuel?
could be a lot of things. I'd start with a battery tester, then starter, then go into the more expensive fixes.
It could be the starter in it. It may be weak or need replaced.
do the bolts on a 1990 pickup truck go in vertical or horizontal
Make sure you are getting power out of your ignition. Check to make sure its going to the "blue relay" or the starter relay or clutch start switch. also, the ground wire is typically a soldered ground connection, mine was broken so you might want to check that, I had to solder it back on and it worked fine.
what is wrong when the truck just turn over and want start.
I would start with checking the electrical system. i.e. battery or starter
It could be the keyswitch or the starter could be wired wrong.
you should try to poo in it
distributor cap
You need to remove starter again and look at the ring gear. Turn engine by hand and inspect the ring gear teeth. Be sure they are not damaged if okay you probley have the wrong starter. some times you have to shim the starter. NEUTZ
Bad starter, bad flywheel/ring gear, bad starter/flywheel alignment.
It is likely to be the starter is not working.