Astra J 2.0 cdti Battery Light

[Wee Willie winkie]

Hi
The head and tail lights were pulsing on my wife’s Astra. I dug out a multimeter and checked voltage at the battery. Charging voltage was erratic ranging from 12.2 to 15.1 under load so I fitted a new alternator. No dash lights.
I fitted a new alternator and this cited the headlight and tail light issue and good readings under load. However the red dash battery light has illuminated
I have checked all the wiring the battery sensor fuse and tried a new known good battery in case the over charging had fried the battery.
I have also checked the belt isn’t slipping and disconnected the battery for 30 mins in case there’s any ECU memory issues. Light still illuminated.
What have I missed? Any ideas?
Tia

[NickCLotus]

Broken connector on the signal wire from the alternator, or new unit has faulty socket.