Aidan;

If Fuse1 and associated connections are in order, a lit AMP light indicates no dynamo output, since this indicator is connected across dynamo output and battery (by way of the IGN sitch and a long path). This is a bit unusual and confuses some...under normal conditions , voltage is on BOTH sides of lamp, and therefore it does NOT light...remember, to light a lamp, voltage must be applied ACROSS it...so when dynamo fails and output goes to zero, IT provides the ground return path...voltage ACROSS lamp resuls, and lamp lights.

You would expect the B+ terminal of regulator to show battery voltage anytime (even when engine is not running), since it's indirectly connected to the battery (see wiring diagram).

No voltage reading on the D+ is again indicative of no dynamo output. This terminal is connected to the B+ terminal by the "cut-out relay" within the regulator. In this way the "cut-out relay" prevents the dynamo from discharging the battery when engine is OFF.

I believe you may have damaged field control of the regulator by leaving it connected when you "polarized the field". My Haynes manual does state it should be disconnected for this. I suggest you try a new regulator to get your dynamo system working again, but you may want to consider one of my alternator upgrades (see: http://www.intelab.com/swem/altkit.htm).

Cheers