I would refer you to the 90 factory service manual. Lookup what items are powered by courtesy fuse. If you have the 90 owners handbook, glove box thing nobody bothers to read, it lists all the fuses and what items get power from which fuse. They can be downloaded for free online various and GM heritage site. Begin with those.
Was it blown before you acquired the truck? Did your mods create this problem? If was blown before mods began , certain items would not functioning, a cause for concern.
Did you use a USB adapter built for splicing into 12 volt power input, with drop-down to 5 volts? Are you SURE your USB is wired correctly,with no shorting during movements?
If you don't have factory service manual with wire diagrams , download here, forum , free. It's your electric best friend.
That's the path I would take. Yeah it sounds redundant, but it's not a water leak " oh hey that fittings loose".
Good luck.