Since nothing turn signal related is working but everything else is, there are limited possibilities. The common denominators for your problem is the flasher and the signal switch.
Your are either not supplying power to the switch via the flasher or the switch is bad, not actuating the contacts. To check this remove your signal flasher, turn on ignition switch, check for 12v at either wire terminal removed from the signal flasher. If you find one with 12v, plug that terminal into the signal flasher. Then check for 12v on the other terminal of the signal flasher, if you have 12v there plug in the remaining wire to the flasher. This would mean you have 12 v through the flasher supplying power to the turn signal switch, assuming the wire is not broken before it gets there. If you do not see 12v through the flasher the flasher is bad.
Another possibility is a wiring error, recheck your wiring.
The best possibility is the aftermarket switch, and when you mentioned Scott Drake I cringed. An buddy of mine replaced 3 SD's in under 3 years, just installed a Ford switch, works perfectly now. If you have to replace it go the extra mile and find a Ford switch, it will be more expensive but it will work.