let me try to explain it. you have 3 sets of contacts in the barrell switch in the R5:
white wire - starter exciter
yellow wire 1 - main ignition live
yellow wire 2 - ignition live but NOT live when cranking
the stereo and other things are connected to the second yellow ignition output, so that when you crank they get switched off while you do it. it sounds like that part of the switch is still working.
the other more important things (like ignition, dash lights, alternator live) come from the 1st main ignition yellow wire, which sounds dead to me.
so if the barrell has a fault it's entirely likely that some things will work and others won't. if I suggest something on this forum it's for good reason, I don't make this sh1t up