I have wanted to do this for a while and I've finally figured it out for the hatch.
96 Mustang tail light sequencer kit $70
Hopkins 48845 12 Tail Light Converter $13
VHT SP888 Red Nite Shades $13
Novita Flasher EP34 $13
2 Relays $11
2 3-wire bulb sockets and bulbs (you can literally go to junkyard and cut them off the brake harness.
Electrical tape/shrink tube
Additional wire to extend wiring.
Okay so wiring is pretty straight forward. Your turn signals only has 2 wires going to it (power and ground). You need to get TWO 3 wire sockets like the ones that go into the brakes to go into the turn signal area. This way when you turn on your lights it'll have power for the big flash, low power for when lights are on, and a ground wire. You can find this at the junkyard and its the exact same socket that goes to your brakes. One thing I didn't mention in the video is that the relays being powered by the battery should have a fuse! Also the brown wires on the Hopkins converter aren't used. The white wires off the Hopkins converter get grounded.
Now for the tail light lenses I wanna say I'm not responsible if you fuck them up... with that being said proceed with caution. Preheat oven to 350 and keep an eye on it. I pulled my tail lights out of the oven after 4.5 minutes. Be careful when pulling the clear lens off because it can crack! I put 4 coats of red VHT night shades on the orange turn lens.
Last thing you're gonna wanna do is change out the flasher relay under the steering column with the Novita EP34 flasher relay to avoid hyper flashing. One way to locate the relay is to turn on the turn signal and listen for the clicking that is happening under your steering column.
My 3rd brake light is on a different flasher that you can look up on your own. Its pretty straight forward on how to wire those. Find the flasher on amazon and a youtube vid on it.
You will get a "Brake Lamp" on your cluster. To remedy that you'll want to buy resistors like the one you'd wire in for LEDs into the original brake wires you cut and twisted together. One side of the resistor goes to those wires and the other to ground. Or if you're like me with a custom cluster you say fuck it.
Enjoy your sequential lights