Kind of butting in here myself, figured I'd throw in some info from what I've gathered around the last few years. I've chatted with a few sim techs when I worked a security gig a few years ago at a FedEx hub...most of them have military backgrounds in some type of electronics field, usually avionics or computer backgrounds of some sort.
Just as an example, I always see an opening for UPS at ANC for a sim tech, here's what their job description and basic qualifications state:
"The Flight Simulator Technician is responsible for repairing and monitoring a variety of simulator specific computer, hydraulic, and visual systems. Technician must be able to troubleshoot electronic equipment to the component level. Technician must have the ability to return to service all simulator equipment, using a broad knowledge gained from job experience...
Minimum of 2 years experience in flight simulator maintenance
Simulator experience including the ability to read and interpret flight simulator software code
Simulator experience including the repair of both hydraulic and visual systems"