Hi Melvyn!
That is another case of "they all do that, Sir!"
The brake light is connected directly to the battery, as is the horn (maybe for reasons of safety, to avoid loss of both by a broken ammeter, dunno). Hence the ammeter doesn't "see" the additional load.
It's not a bug, it's a feature
Cheers, Markus
P.S: Am willing to give your bikes a good new home in my garage if you can't live with the way they are wired
PPS: Alan was faster. May I still have the bikes ????