Charlie, it's been way to long but I remember working on a Cougar with sequential turn signals, there was a small unit in the trunk, it held a motor that would turn a set of contacts that would "fire" each lamp. I don't remember where it got power from, but it may be something to look for.

Under edit, it was located right below the lamp if I remember it right... but this was in 80 or 81 I'm thinking....