That left side safety should have a small spring and a small plastic piece that the spring pushes forward against the shaft of the safety. That little piece is what gives you the "click" and holds the safety in position when you move the safety lever.
Sometimes that piece and the spring fall out/off when you remove the safety. You have to be on the lookout for it and make sure you reinstall it if it does fall out.
Actually, look at TOK36's pictures. The detent and spring push against a small "pin" that is out in front of the shaft and controls how far up/down the safety can be moved.