Doors unlock but don’t lock
 

Do you have any aftermarket wiring or stereo on your rig? You think the doors were taken off at any point during the lifetime of the truck? [eg. for custom paint or wrap?] Custom fob/alarm system that overrides the factory setup? [Viper, etc]

I suspect the wiring harness along the line or switches, you would need to do a drop voltage test along the harnesses involved. I'd bypass the harness and run the ground and +12/-12v to the switch directly and see if it works. That would eliminate the solenoid/motor being the problem. If it works fine, then you check the test the two switches [center doghouse and door mounted, you can swap them with new ones or use known working ones from other doors], after that it's going through the harness and checking for damage or internal wire rust. [A drop test will reveal this].

The reason I mentioned door removal/paint/wrap is that some body shops cut the factory door harnesses instead of unplugging them at the 4/6pin jumpers and then splice them back together. I had one shop do that on my truck and it caused all sorts of window/lock performance issues. I wound up going through the whole system and crimping up new connectors/wires to get everything working ship shape again.

There is an aftermarket stereo and the truck was painted at some point before me. I don't believe it's the solenoid, all locks were working fine, and then I got out of the car to lock it and none of them worked all of a sudden, so I tend to think it's more in the relay - at least I hope! I don't want to chase down a pinched or loose wire somewhere!

I realize this is an old thread, but did you every find the problem. I am having the same one