Ive had something like this before, like Blue says switches and wiring. If it is the switches they can be pulled apart and cleaned up, this works for a while. Bit tricky to get back together but cheap fix. Else you will need to get it apart and splice some fresh wiring in between the body and door.
If fixed my issues by cleaning the switches but was sat in a traffic jam on the M6 on a stonking hot day, wound down the windows and thought I saw something float through the car. Then looked down to see thick white smoke pooring from a switch. Turned out that the drivers side jammed on and started to burn out. Had to rip the switch out real quick to avoid a fire

Decided to go buy a new switch, wasnt that much, might be the way to go
