Thanks John... it was pure coincidence that I was working on a bike* with that symptom recently. Really glad (motod) Rob has the end of his frustrating electrical journey in sight
Personally I prefer to use crimped, good quality (Japanese) bullets for alternator to RR wiring with a smear of contact grease to minimise corrosion risk over time. Easy to poke through engine case holes if needed and plenty of contact area to carry that current. The bigger problem is cleaning up the oxidised conductor strands on 40 year old wiring.
When I first saw a Deutsch connector for this application I wondered. Pins are rated at 13A but I suspect the genuine 4 way crimp tool at over £400 is essential to reliably achieve this. There are much cheaper 3rd party alternatives...dunno how good they are.
* The get him home repair employed twisted wires and insulation tape