[BAracer]

So...

Removed the digital power base and lap counter from the circuit and the car now runs at speed round the track using the original controller (although in the opposite direction to the digital cars, but am assuming that's can be sorted at the guide connections).

However...

When I plug the scp in, without touching the trigger, the car creeps forward in the 10 seconds before the base light goes out. Pulling the trigger during that time has no effect on the speed.

Swapping the Ninco plugs around cuts out the base light instantly in a couple of combinations. I have reverted back to the arrangement in my picture.

Off for a boxing day walk shortly, then will get down to business later!

Thanks for the advice so far Alan and Andy.