Got charging problems (ie a lack of) on my road bike, ZZR600.

Changed the regulator/rectifier unit no difference so set about checking the
alternator output. Disconnect the reg/rec unit and meter the alternator
wires and I get 5v at idle increasing to nearly 60v at about 10k rpm, same
across all three wires. Haynes book states spec of 45v but doesn't state at
what revs.

Now the really odd bit that stumps my limited electrical abilities. Plug the
reg/rec back in and check the alt wires at the same point and I get 3v and no
more. Resistive and continuity checks on the alt are normal.

I'm guessing it packs up under load.

Have you checked all three stator wires to ground?

No, what reading would I expect to get ?

You shouldnt get one, anything leaking to ground is a fault, I had that problem on my R1, the week after the warranty ran out, a new stator is required if there is any reading.

Checked to earth and is ok, no continuity.