Grrr! I spent today tidying up some wiring on my A and B registers and building the Instruction Register. Everything seemed to be working fine until the B register started acting up. Reading data from the bus is way, but when I enable to the output latch, not all the bits get put on the bus properly. I bit of poking and prodding at the wiring and sometimes (but not always) the data will appear. I know it isn't a power problem - I have checked the power distribution and it is nice and stable across the boards I have connected so far.
The culprit is most likely the wiring. I have been unhappy with one of the spools of hookup wire I have - the wire is difficult to work with and tends to break too easily. I need to toss the spool and replace the wiring, but that is not so easy. Where I live it takes around a week to get anything via mail order (even longer if it is from overseas) and there are no local electronics stores I can turn to. Plus I'm going away next week... In the meantime I will use a different colour (I like to colour code my wiring and I don't have any spare colours (yet)) to confirm that the wire is the problem and replace it (again) when I am able to get some new spools of hookup wire.