CorkyShark, welcome to HDTimeline and your first troubleshooting "exercise". What others are trying to say is you need to determine if the turnsignal lighting is filament type (stock) or LED type (aftermarket).
1) Turnsignals all stock means the front signal lights one of the two filaments in the front; the rear signal lights use single filiament lights. What that means is the fronts have "running light filiament AND a signal filiament", the backs have a single filiament that only has a single turnsignal filiament, with the brake light coming on when you hit the brakes.
If stock setup and you have checked the bulbs by swapping right to left, then new one(s) if you find the offending one and your good. Check and make sure there is no corrosion or misallignment or wrong bulb used, clean contacts and use dielectric grease before you put each one back together. Wiring, corrosion and pinched/cut insulation are the most common problems and in that order. If all else fails, then you have a bad TSM/TSSM module which runs...you guessed it about $150...!
2) If you have LED type bulbs, someone replaced the turnsignals BEFORE you and may not have added the recommended load equilizer (simulates load of filament type bulbs), and never got the problem fixed just right, and if left alone it can "fry" the TSM/TSSM. Hopefully you have not gotton to this point and have to replace the module.
