914F generator/ammeter query

Unless the display is Blank;  The Ammeter is never,"... not showing any reading."  Zero is a reading!

If you see more than 13.8v on the battery, Engine ON, the battery is charging.
If you see less than 12.6v on the battery, Engine ON, the battery is discharging.
The ammeter will either display the charging current or the discharge current. Typically 2 to 3 or more amps either way.
If is does not show a discharge current before starting, Suspect the Ammeter.

You may need to temporarily extend your meter probes for safety sake.  Any wire will do.
The B+, R, and C Terminals on the regulator should measure slightly more than the DC Battery Voltage, Engine ON. Ground referenced.
Most importantly, they should ALL measure the SAME.

If the Regulator terminals do not match the battery; suspect an open fuse or switch.

If all else fails, the G terminals on the regulator when disconnected, Engine ON, should measure 10+ volts AC at idle and 20++ volts AC at speed.
AC not DC!
Measure from one G wire to the other, not to ground.  (G = Gelb = Yellow in German)

Point taken re ammeter, it is an analogue dial and perhaps it would be more accurate to say no movement in the needle even when adding to, or reducing the load on the electrical system.

Thanks for the other thoughts - we will see where we get to.

Cheers

I understand you to be saying that you have an analog (mechanical) gauge that reads zero whether or not the engine is running and regardless of the load. If that is the case, seems to me that either the ammeter is bad or it’s connection is bad.

If I remember correctly, the ammeter should read neg, depending upon load, without a generator.

Don't concern yourself with the Ammeter until you get the Volts correct.
Once the battery volts rise significantly above 13 volts, the generator is producing charge power. (~14.2 is ideal)

The Ammeter is really a voltmeter that measures the voltage across a very low resistance shunt. 
Many Ammeters have the battery current pass directly through the meter itself on large gauge cables.
More sophisticated ammeters have the shunt mounted remotely and the Ammeter connected by relatively small gauge wires.

In either case, the idea is that by placing a small resistance shunt (0.01 Ohm), essentially a very high wattage resistor, in series with the generator cable, the voltage drop across the resistor will be proportional to the current (Amps).
10 amps would produce 0.10 Volts and the ammeter scale might be labeled as 0 to +/-50 maps for 0 to +/- 0.5 volts.

Thanks guys. Issue finally tracked down to a poor connection in one of the relays. Ideally need to replace the connector, and relay but getting one out of either Rotax or the airframe manufacturer seems more of a challenge than it should be! 

thanks again