Didn't think of the jumpers - MK1 is quit a long time ago. J1 (the jumper for datasette motor voltage) might be another choice if you are using a 12V VIC. 12V can also be taken from the coil L4 near the SID, left of the keyboard connector: The upper terminal is 12V.
That's really helpful Jens, Thankyou! Yes, it is a while ago. The board is serial# 08