i have been trying to get this problem sorted out on my a6 

on the alternator there is a plug it has 2.pins in the.alternator but the plug from the that plugs in only has one light blue wire is this correct i will try and post a pic of them both cheers

plug has one pin alternator has 2pins 

measured volts and its 9.8 volts in wire

 

all help appreciated cheers

That would seem to be correct as it's probably the voltage sensing wire that energises the alternator and puts the charging light out once there is a charge occuring.

 

Voltage regulator is faulty in your alternator easy to replace, You will have Partial Consumer Shut-Off errors flagged in BCM and ESP fault on dash after approx 10-15 min from starting engine.

The pin which is connected (light blue wire) is for the warning light ("L" connection)

The other terminal is not used on your car. It is for the Digital Field Monitor, which connects to the ECU on some vehicles and provides information on the alternator load.

For more information Google "regulator terminal guide"

 

I just saw your other post on your alternator. When your alternator was replaced maybe the DFM was not connected.

Suggest you reconnect the DFM pin if appropriate.

 

sorted it cheers lads previous owner used cheap alternator fixed by replacing with valeo cheers