I had this problem too. My solution was to remove the ABS light from the dashboard because Ford wanted $4000 Canadian to fix it. (replace all ABS wiring and module).
Since then, my ABS seems to have been working properly, but I haven't put in the ABS light again.
My theory on this is that the ABS module needs a constant voltage on a certain pin. If this voltage drops below the amount it needs, then the ABS light comes on.
When you put on your A/C, then the voltage drops below the threshold and the ABS module freaks. For instance, the radiator fan runs when the A/C is on. Maybe this causes the drop in voltage.
Anyway, I think the wiring on our old cars is poor and there is too much resistance somewhere. This causes the voltage to drop when the current draw is high in a particular circuit.
If you are under 100,000 miles, then you qualify for replacing the wiring in your engine compartment under recall, as long as Ford determines the wiring is bad. I have way higher mileage, but give it a shot. Many problems have been solved by replacing the wiring, but it is expensive and time consuming to do it when not under warranty.
- Randall
