Update:

With slider at TAC = spindle fires up to high revs and sometimes trips my supply RCD!
If it doesn't trip the RCD, I can usually (not every time) start/stop the spindle in VR5, but not alter rpm.
With slider at AVF = spindle fires up to lower revs (1k rpm?) then stops.
I am not able to start/stop the spindle in VR5.

Wires #54 & #55 removed from Sprint1200 = spindle does fire at all
Wires #54 & #55 linked out on #1 & #3 connector on Sprint1200 = same as with #54 & #55 in position (incl same with the TAC/AVF slider)

At startup, both TAC/AVF, I measure 11.5v across #54 & #55

The only spindle settings I can see in VR5 are max/min rpm, and check boxes for manual, speed pot & external speed pot...

Help!