OT : RJ45 Telecom wiring

Can anyone suggest URLs, etc that give the wiring of RJ45 sockets. in telecom applications. Not 10bse<n> (which from what I understand are not strictly RJ45's anyway), or ISDN, but older telecoms. The web pages I've found soe far give the wiring for up to 4 POTS lines on an RJ45, which is, again, not what I am looking for... In particular : What pins would I expect to find a normal 'switched' telephone line on (4 and 5, I think?) What about a 2-wire leased line ('private circuit')? Or a 4-wire one? Why would there be a resistor of about 866 ohms connected between pins 7 and 8? Why would pins 3 anf 6 be shorted together? In case anyone's wondering, I've bought a non-working telephone line simulator, and am trying to make sense of the numerous relays connected to the telephone connectors, which are RJ45s (genuine RJ45s, with the extra polarisation notch). Books on US telcoms practicce are few and far between over here... Thanks in advance for any help...