Thanks for the replies, I got it sorted now.
Here was the problem for info.
I unsoldered the 2A transistor (FZT 753) and checked it with a meter, it was totally open circuit from Emitter to Base. A new transistor from a local electronics shop was 85 pence. Fitted this and now works great. Answering my own last question, when the ignition is on the clock is at full brightness, when sidelights are switched on the brightness roughly half's (with dimmer on full).
So the clock lights rely on this transistor for daytime illumination (approx 1.8V on the base of the transistor) switched by the black ignition wire signal (but actual votlage to the bulbs supplied by the red wire via the transistor). Then when sidelights are ON the transistor is switched off and the bulbs powered by the Gray with Black tracer wire (normal spedo lights via potentiometer)
Only other thing to add that caused confusion is when the clock has been totally disconnected in this way, upon re-connection it will PERMANTLY illuminate (ie even with ignition off) until the clock time has been reset, then will function correctly off the ignition key.
Thanks again