You have problems with your steering generator Look first the wiring from generator to your A 5 Card
Look after wiring 62 and 63 On A5 Card you will see numbers and leds Connector numbers 701 and 702 on print when you steering you will see that the leds on that position go on and out.
The 48 Volt for steering is 1001 Cable number 25

But mostly always the tachogenerator is not good you must replace it You can open it and cleaning it but the fault will come back soon.

Regards

John.