Originally Posted by decca1o

I would guess that it is not the charger.

Originally Posted by yorkie_chris

Check the voltage to the battery, it should be 13.5 to 15.5 at 5000rpm with the lights on.
If not, check the red wire that goes to the RR has continuity to battery live and the black has continuity to earth.
Then check the alternator output, should be 70v (AC, not that I'd ever forget that...) between each of the yellow phase wires and any other.

Originally Posted by timwilky

Measure the voltage across the battery 30 mins after a charge
measure it again with the engine running at about 5000 rpm and lights on
the above is sufficient to tell us if the charging system is working or not.
I would expect to see something about 13 - 14V.
If not. disconnect the 3 yellow wires going into your RR
think of them as a,b,c. Turn your multimeter onto the ac voltage scale and measure the voltage between ab, ac, and bc. you should be seeing something about 70-90v. from the alternator
if the alternator reads ok and you are not getting the charge to the battery it is a goosed RR. Go out and buy a nice one from a Honda. muller the connections to fit. or source a reputable pattern part.

If the initial check was ok and you were getting the 13-14v. Leave the bike overnight and measure the voltages again in the morning.