Ford Repair Questions? Ask a Mechanic for Answers ASAP
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Back then, these Escorts had problems with the negative battery cable terminals getting loose and causing all kinds of problems just like the ones you describe. Since you've checked the power side of the circuits and found no signs of trouble there, why don't you give the ground side a good look?
Now, I know that anything can happen with these electrical systems, so, if a good visual inspection turns out to be not sufficient to find the problem, you'll need to get yourself a multimeter so we can take it from there.
Please let me know what you find.