Progress made, but still no brake light on left

did you take the bulb out of the right side and try it in the left side? each bulb socket has to grounded. some times it takes a few twists with the bulb to get a good connection. from my lighting dilemmas (and i have had my share believe me) , the odds of two different signal cancellors having the same issue are against you. i have had many brake light/running light and signal issues and 90% of them have been bad grounds, corroded/worn out sockets and bad bulbs.