Well done 2+266,
I had a similar problem when I first had my car with blinking headlights, turns out that halogens were installed without relays. I had them installed and the transformation in lighting was fantastic, and the blinking stoprd too. You need a decent electricion to make sure all the wiring is right, including the dip switch.
There's a great 'how to' article in mustang monthly on line that gives you a good heads up.
Many happy years of driving to you.
Cheers Bee