Our vintage bike got converted to 12v in order that it could handle a modern starter motor ,which for a 350cc single is quite an advantage . But we did have to replace the old plate rectifier with a modern solid state bit of kit ,
But we digress!

Linking those terminals Inee had no effect but the 24 v supply was not there . There was however 20v at the input of the missing fuse and it looked like the output from the rectifier headed in the correct general direction, so took a risk, replaced the fuse , and switched on
A 24 v led lit up on the board and lo the spindle functions all seem to work as we would expect.

I will post the requested pics you ask for Inee but too late tonight .

Traverses do not work yet, regardless of the position of the Manual switch but someone did say it would be surprising if traverses worked without a computer connected so maybe that should be next step,
I did manage to get hold of the "Boxford engineer " who owns up to not having proven the functions before the machine was sold . It seems he was a factory mechanical fitter and whilst they were trained to carry out limited electronic testing, he relies on an electronic specialist as he needs one.
He does however have a number of spares so might be worth knowing .

One thing he mentioned was that he thought there were traverse limits , to prevent crashes , and it could be that these might be operated .
I will check that tomorrow .
With a serial connector on the machine, I presume there must be some breakout function within the boards. Might it be time to connect a computer and see what gives.
Will it matter whether we are running Mach 3 or UCCNC? I guess we will need to know pin identities, etc but I will not go there until I have the benefit of your invaluable opinions

Looking forward to those .