So, i put a starter in a couple of months ago. A couple weeks ago i start my truck and the starter never disengages. So i put in a new starter and solenoid. Monday night it does it again.
So i just put in a new starter. Anybody have any ideas what could be causing this. Its an 1989 4x4 4.9l 4 speed.

 

Trouble-shooting is a bit easier when you replace parts one at a time. Only do multiple repairs at once if you had to dig to get to where you are working.

Regardless, it sounds like the problem is not the starter or the solenoid. Check all of your wiring first. Then I would check your ignition switch. Take the steering column off to get to the switch contacts. Figure out which contact is responsible for sending voltage to the starter solenoid. Also figure out which contact is +12v constant. If you need an explanation of that just let me know.

Disconnect your negative battery terminal so the truck won't actually start. Put an ohmmeter on the two contacts. Turn the ignition key to the start position, and hold for a few seconds. Release. You should see resistance (ohms) drop to 0 when you turn the key, then jump toward infinity when you release it. If resistance stays at or near zero, it's a faulty switch; replace it. If the problem is only intermittent, the switch may not fail the test the first time. If that is the case, don't rule out the possibility of a faulty ignition switch until you've repeated this exercise a couple dozen times. And if you're still uncertain, it couldn't hurt to replace the ignition switch.

 

If you pull the small wire off the solenoid powered from the Ign switch, the starter should disengage & your problem will be ahead of that wire, probably in the ignition switch itself as mentioned.

 

^ Try this first. I was over-complicating it.

 

But thorough!