This is nicked from UKMOC but Ducati electrics are similar to Aprilia. Good guide anyway.
First a basic troubleshooting process to determine whether you have a charging system failure.
A good Multi-meter is a pre-requisite.
Record your battery voltage under the follow conditions
1) Ignition off, unloaded battery.
2) Ignition on, headlights on, not running
3) Bike started, running at idle
Condition 1, should be at least in the high 12.x range if fully charged.
Condition 2, your voltage should not drop much below 12.0 at worst. (It may continue to drop – hopefully slowly! – As your lights will be discharging it. However this should be a slow decline)
If it does drop immediately into the 11’s, your battery is insufficiently charged – if it was just charged from a battery charger however, then it indicates your battery no longer has sufficient capacity to retain charge/supply current to load and should be replaced.
Condition 3 is what we are most interested in with respect to charging capability.
Voltage should be at least in the 13’s at all engine rpm. You may detect it will fall off slightly as you raise engine rpm. This is not atypical performance. A simple mod that can enhance your charging voltage to the battery can be achieved by this modification outlined in this thread. That should give you performance in the 14V+ range.
What if you have less than 13V?
First thing to check is the fuse in the charging circuit.
Next, examine the wires and connectors between the R/R output and the R/R input – are these charred/melted due to excessive heating? This is fairly common result of poor connection between the terminals.
A ‘cold’ resistance check for shorted diode/SCR:
Unplug both input & output plugs from R/R;
With your meter set to read resistance (use a diode test if the your multi-meter has one), test from each pin of the three pin plug, to both the red & green wired pins NONE of these should read short circuit (zero resistance); depending which way you bias the test leads, you may get some reading (from the forward bias) but it must absolutely not be a short. If you see a short on any of these readings the R/R is defective.
Next, do a resistance check on the stator (check at the cable connector going back towards the stator itself).
Measure between the three respective combinations of the three pins:
1-2
2-3
3-1
This time each of these should measure almost short circuit (very low resistance in order or about 1 ohm)
This next check is probably the simplest/quickest way of determining a stator problem - in majority of cases a bad stator will be indicated by failing following test:
Check resistance from any one pin to the engine earth – this should not read any indication – maximum resistance or open-circuit.
If you read ‘short’ in that last test, then your stator is .
(if open, it is not quite guaranteed your stator is good however - but in majority of cases a failed stator will fail this isolation test)
