Car: V70 1999

Symptoms:
--DISconnect doorlock connection to the master window switch , all doorloaks operate using the driver door keylock
--connect doorlock connection to the master window switch , all doorlocks go to the locked position and won't budge from there
--at the same time this started, the fuel door release stopped working
--windows work normally whether doorlock connected/disconnected (both from master switch and on each other door)
--about a month before this started, there was an antitheft or immobilization code that appeared, then never appeared again

Thoughts:
since other doors and driver door operate with the keylock, the door wiring harness is ruled out. also, mirror controllers, speakers, lights on driver door work

Question:
is there reasonable certainty the problem is the master window switch only?
would it be easy to just replace the doorswitch module of the master window switch rather than the whole doorswitch module (where the replacement comes from a used switch)?

Thanks.