Check all ground leads , positives and negatives on the battery and from the alternator, to the body.
and checking does not mean tightening them, it means taking them off, wire brushing the bolts, cleaning painted area down to clean metal etc. as at 11 years old.
if that does not resolve it .. look at replacing the ignition switch
where are the ground leads ?
see BEMM Manual here
page 192
https://www.nl.ford.be/content/dam/guxe ... sit-2T.pdf all the best.mark