It was recently pointed out to me that only one of the tail lights works when the brakes aren't engaged; however, they both work fine under braking. It sounds like maybe there is a bad switch somewhere. any ideas?

 

Sounds to me more likely that the filament for one of your bulbs in gone. You have two filaments in each bulb. One illuminates for indicating braking & the other illuminates when your lights are on. Both the front & rear brake light switches make both bulbs light & the bulbs are all on the one relay.