Hello joanbmat, and Welcome to the site! Sad your friend passed, but The Love Machine Lives on!
Alas the Conversion Vans are not in the best of shape, and wiring issues are common. Short circuits, faulty grounds abound. Trace what you can with a test light and ohm meter. The factory wiring diagrams will show the conversion provision for auxiliary wiring, such as tow and conversion packages. This will indicate the 12 volt source location on the vehicle fuse panel.
Some conversions have a separate auxiliary fuse panel, my B350 Campervan does, the B250 Conversion does not. All of the wiring is buried in cabinets, behind panels and in bulkheads. Not easy to troubleshoot.
There is usually enough Spaghetti contained in Van conversion wiring to feed a small family. It's amazing. So study the basics, and proceed logically.
I'd get a hold of a factory service manual, and lubricate the snot out of that window regulator first thing. Motor may be toast, but a lube never hurts. It probably needs it.
Go Love Machine!