Wiring was done as below ... and it works, just can't teach it the gears.
SU* ........ DG8 ...... ZXR400
Red ........ Red ....... Brown on Tacho (+)
Green ..... Black ...... Black/Yellow on Tacho (-)
Blue ...... Orange ....
............ Brown ....... Yellow on Pickup Coil (originally Black on Tacho)
............Green ... .... Light Green on Neutral Light
*= speedo upgrade kit
Dave @ Acumen thought the tacho pulse is too "dirty", so I rewired it to the yellow on the pickup coil, still no better.
It will learn gears 1 to 4, but I run out of road trying to register 5th

I find that as a "recovering" car driver that my brain just won't attune to cruising at 7-8000 revs so I'm forever - embarrasingly - looking for more gears, hence the desire for an indicator.