rectifier/regulator

[Drummie]

Hi Caulky, thanks for the much appreciated info. I have connected up the rec/reg with the exception of the BLACK wire from rec/reg. I take it this wire connects to the BROWN/WHITE wire, that I have traced to the ammeter and then on to the battery (positive earth bike). In my head this makes sense as the ammeter needs a feed to indicate if the battery is charging, but just checking for peace of mind.
The battery is definitely past it, but I also think the old lucas rectifier has had it too. the plastic coating has melted, blistered and fallen off. If I find out that the alternator is on its way out, I'll replace it and the rotor and maybe go for the 6v coils too. Drummie.

[Caulky]

I don't have a '66 wiring diagram, but bikes fitted with an ammeter are basically similar.
Hence, whatever the wiring colours are, you need to wire it as below:
From the negative terminal of the battery-to fuse-to *ammeter (-ve). And nothing else except,
At this point * there MAY be other high current stuff connected, which would otherwise drastically affect the ammeter reading, in the short time, (horn, horn button).
Now, to the OTHER side of the ammeter (+ve), the ammeter needs to detect which way the DC current is flowing, to/from the battery.
The output of your rect/reg (black) is connected here, and also the ignition switch.
The ON side of the ignition switch has the EI white wire.
There are variations, and I wish I could be more specific for your bike, maybe someone else can chime in.
i.e. the lighting switch could be before or after the ignition switch, depending on whether the lights can be turned on without turning the ignition switch on.
But the lights need to be included in the other side of the ammeter.
My '71 A65L was not fitted with an ammeter, but it is now.

[Drummie]

Thanks Caulky, your info and time is much appreciated. Its wired up as you said, with the lights only working with the ignition switched on, although the horn works with it switched on or off. I've traced wiring from ammeter and light switch throughout and wiring from rec/reg, to get a better understanding of it. I have also disconnected the Zener diode, so hopefully good to go now. I've found wires have been replaced/added here and there with different colours but fortunately I've been able to trace where they're going and coming from. Thank God for the multimeter. Hopefully I wont be pestering you on this subject again. Cant guarantee I wont on other problems I come across haha. Again thanks for your help. Drummie.