I just replaced an old mains smoke alarm with a BRK 660 MBX. Now, the old one had a green light on all the time, this new one i needed to change the baseplate as well, as the connectors were different, so i pulled the wires down through the hole from the ceiling, so i had three bare wires, brown, blue and white, screwed the baseplate to the ceiling and loosened the small screws so i could put each wire into the connection, blue wire opposite the blue wire in the baseplate, brown opposite brown wire and white opposite white wire. and tightened the screws, now, this white wire from the ceiling had fallen out of the ceiling with some yellow and green tape around the end of it that disappears in the ceiling, the tape wrapped around a plastic thing, and on one of the rafters was another plastic thing screwed to a wood rafter, so i pushed the taped end back into the plastic yoke on the rafter, guessing this was where it was in the first place. the smoke alarm is a push fit with a battery back up. i turned the fuse back on at the fusebox, the red light blinked every 45 seconds for the battery, but the green light only came on when the light switch was on. Does anyone know if why this is happening, is it something to do with the white wire. the old one worked perfectly, the green light was always on, even when the light switch was off.