This is an age old problem of the Fabia. Pretty well covered on the site but hoping this can be made a sticky and then be pointed to or easy to find.

If the battery light fails to show, the ASR light comes on after 10 mins or the alternator isn't charging its well worth checking the DFM wiring. This wiring is a signal from the engine ECU to the alternator. Without this the alternator may not charge. There is a black plug in front of the gearbox in a metal bracket. The plug carries two wires, these quite often break or corrode. Simple fix is to cut out the plug and any corroded wiring and join in two lengths of wire to join them up again.

Edited 13 January13 Jan by Tech1e
Added image

Usefull to know. especialy as my asr light is perminently on ...