Alternator problems

Hi, and thanks for all help.

My Fabia Mk2 2012 1,2 tsi have a problem with the alternator. Or?

12v about batteri when car is running, and about 12v stopped. Batteri lamp is coming on in the dashboard. 

I measured about 4,8v on the alternator. 

I know replaced not just 1 but 2 alternators, the first one was used, so i thought it was bad, i decided to replace it with a new one! Still same problem! 

No i checked the 2 small wires from the connector on the alternator, 1. To the ECU, made a bibtest, no problem.

And the other wire a blue one, goes inside the cabin to the BCM, made also a bibtest.

Does the BCM controls the alternator to produce power? I mean if the BCM is bad, so the alternator not will produce power? 

Sorry for my English, im from Denmark, and found this forum? Maybe im lucky.