I want to replace both a heat detector and smoke detector in my flat. The detectors are linkd to a central system for the building and all flats. I've managed to disable this for the change and having boughtnew ones from Screwfix, took the covers off the old ones to find the attached. The Screwfix ones come with no instructions, so I'm guessing that all detectors have a standard 4 connection wire fit. If so, how do I know what wires to connect to what with teh new unit?