replacing room stat on honeywell y fully pumped system

[unclefewst]

Hi , i wonder is someone could give me some advice, it relates to the wiring for my fully pumped honeywell Y system which incorporates a 3 way mid position valve with a cylinder stat and a room stat, the system i put in myself in 1986 and has served me well, however i did not wire up the electrics (looked a nightmare for me ) and the electrician who did it i have lost contact with, the question is this i would like to replace my honeywell T6360 room stat (it is the rectangular one in green with a dial on the front, inside there are four terminals 1,2 3, and 4 from the top to the bottom in that order, there is no power to number one however there is permanent live to terminals 2 and 3, and terminal 4 is the switched live (when i turn up the stat terminal 4 becomes live,
This is what i would like to do i wish to replace this somewhat outdated stat with a new horstman centaurstat 7 but i am not sure what terminals i should use,
before you say anything the terminals are not colour coded, the cable i aquired at the time was/is heat resistant butal numbered 1 ,2,3,4, hence that is how it is wired up,
any suggestions would be gratefully received

many thanks Dave