How many wires dose your signal switch have? this info might help diagnose your brake issue.
See Cletis post above....Your brake lights might work thru your signal switch.
My aftermarket 12 volt heater motor has one orange and one black wire like yours. Mine is a "Unimotor" brand. one speed, reversible.
If your motor is like this check the direction of rotation. if it’s running backwards simply reverse the wires. One wire power, other ground. You can grab power from your new fuse box if there is room. Check your motor label for amp draw and fuse to protect. The heater switch I posted gave me 3 speeds and is lighted
When your tested your bulbs did your ground them? The originals are grounded when placed in gauge housing. If you did ground them, and they didnt work you will need to meter your headlamp switch.
When you pull your headlamp switch out to the first position you should read voltage on instrument post of the headlamp switch.
Is your alt internally regulated?
Someone else might be able to assist you with your ammeter hook up. I’m not running one.
What helped me when I wired my 50 was to draw out each circuit on paper. It helped me visualize what was going on.
for your horn you can grab power off your new fuse box.
I believe factory set up came off ammeter post.
it soulds like your fuse box is hot reguardless of key position. So your horn will sound key off
Are you adding a horn relay?
This will be very rewarding for you when its complete.
Oh and dont forget the bulb for your hi-beam indicator. you need 6 bulbs for your instruments/ignition
Good luck
