Managed to get some time working on the bike today. I replaced the pulse generators but they made no difference so I started looking at the headlight wiring. Disconnect right headlight and voltage still drops, plug it back in and disconnect left headlight and voltage doesn't drop. I noticed the right headlight plug and wiring has been replaced but not the left so it's probably the wiring for the left light. Both bulbs are the same 35/60's.

I have been waiting for Dmr in Japan to release their updated wiring harness which they have just done so I've ordered one of them which they have just shipped. Hoping the replacement loom will cure all the problems in one go. I'll report back when I've replaced it. If you're after a loom I went through Webike as I have used them before, they're cheaper than Dmr and Jauce and it's less confusing.