How to fix brake lights in my 98 Lumina Sedan and turn and tail lights work new brake light switch and wring to the bulbs are OK what to do now?

I also have a 98 Lumina Sedan with the same problem. I did the full wiring check and finally narrowed it down to the turn signal switch. I noticed that if I signal for a right turn and apply the brakes, the left brake light comes on. The turn signal handle seems a bit loose but the brake lights work if you hold it up briefly (like to make a lane change to the right). Replacement part is GM OEM # 19005031 (AC Delco D6226A) for cars w/o the radio accessory on steering wheel. If radio accessory on steering wheel, GM OEM # is 19005032. It takes 90 min to 2 hours to replace (shop time at dealer is 1.4 hours).