The tail lights are a separate circuit
Originally they tie into the headlamp switch on the Tail lamp post
As long as you have power and pull the headlamp knob they will work.

What bulb are you using for parking lamps?
You should have two wires off each parking lamp.
Wire the brightest light to the turn signals
Right front to red wire on your 900
Left front to green wire on your 900

A dim light could be a bad ground or you used the park lamp wire


Take the two wires off the stop switch on the firewall, touch them together and see if the brake lights come on. They should as long as you have voltage. One of those wires should be hot.