Flickering Fix
I just fixed that exact problem today. It was my headlight pull switch and wiring harness. There was a recall on the switch and wiringing but on my '90 SC, the recall was not active anymore. Got to
http://www.ford.com and click on the link dealing with customer service or somthing like that. There is a recall page that you simply plug in your VIN and it will tell you exactly what active recalls are on your car. If it is not on the page then you have to fix it yourself.
So, to get to the switch, take of the driveside portion of the dash (obviously).
It is very easy. First pull the headlight pull switch knob off. Just pull. Next, it might make it easier to pull the dash out if you first take off the housing around the steering column. Directly behind the steering wheel in a small housing about two inches wide. Take that off by pulling out on the seem on the left side of that housing and then take it off. Then there are three screws on the underside of the main steering column housing.
Next, there are two philips head screws under the overhang on the dash. After you unscrew them, just pull then whole front part of the dash out. It easily pops. There are just small metal retainers that hold it in place. Now your switch is easily exposed just unscrew the aluminum nut on the front off the switch and pull the switch out from the whole on the side there.
On my car, the red/yellow wire was blackened at the connector and the plug was cracked and charred brown. Unreal!
To make sure, after taking of the dash I ran the car with my lights and fogs on until they started blinking. Sure as hell that wire was as hot as hell and when I tapped on it, it would flicker as well.
The switch itself might not be bad but, they redesigned it because of this problem so I'd get the switch as a well as the wiring assembly.
part # Motorcraft SW 5543 for Wiring assembly
part # Motorcraft SW 5542 for Switch
With the wiring they give you the crimp locks so you just have to cut, strip, and splice the wires and plug the other end it and your done!
I hope this helps.
Peace,
Anthony