I presume the missing link is probably the ambient light sensor that controls when the keyboard lights up. I don't know which other part or assembly includes that sensor, in the models that came with it installed. Call one or more of the parts vendors listed below (phone #s are on their web sites) and ask exactly what you need to accomplish the result you're aiming for. They'll know.
http://www.pbparts.com (parts and repair work)
http://www.dttservice.com (parts and repair work)
http://www.powerbookresq.com (parts and repair work)
http://www.powerbookmedic.com (parts and repair work)
http://www.tekserve.com (parts and repair work)
http://www.ifixit.com (parts and excellent, illustrated online take-apart instructions)
Prices and availability of the same parts can vary widely, so check around.
TiBook 1GHz/1G/120G; PTProG3 500MHz/768M/160G Mac OS X (10.3.x) film and flatbed scanners, projector, graphics tablet, laser and photo printers