Although they don't appear to be shown in the wiring diagram, there is always a connector at the tail lamp, especially handy for the drop off or hinge up mudguard tail piece.... On an M20 I think there is also one on the main battery lead above the battery.
The connector is covered by a slide over piece of rubber tube. Here's an original on my James ML. Ron
I have manages to source the wire locally in Hong Kong so I will buy this end instead, it will save on the postage as well, they actually have 108 rolls in stock if you run out in the UK.