[tdz840]

Pigeon
Many thanks for your help on this.

I have both regulators (dynamo and alternator) in front of me and the terminals available on the dynamo regulator is D+ (Dynamo), DF (Dynamo field), Earth (D-??),and B+ (Battery).
Dynamo regulator
On the B+ (Battery) terminal are two heavy gauge brown wires which looking at the wiring diagram one goes to the starter motor and one to the fuse box.
The D+ terminal also has two wires one goes to the dynamo D+ and the other goes to the charging light.
The DF terminal has one wire which goes direct to the dynamo.
The earth terminal obviously is part of the body of the regulator but has a dedicated screw for positive location.

Alternator regulator (new)
There are three available terminals DF, D+, and D-
From your diagram D- is earth, DF is the field terminal and D+ goes to the alternator and the charging light. All good so far - but wait!! What about the B+ terminal?? Theres no B+ terminal fitted on the regulator I have and according to the Haynes schematic appears to come from the alternator only.

Finally looking at the P1800 scematic in the Haynes manual (page 196) one wire from the dynamo(B+?) goes to the lighting switch (37).

Sorry for being such a plonker but I dont want to reconfigure the wiring, connect up and watch it change to a molten blob!!

In anticipation
Russ