Gavin,
One other thing to check is a faulty voltage regulator. It's located on the firewall and can be replaced by a $25 part from Canadian Tire (or even a Ford dealer if you have one that isn't totally stupid about not having a current part number).
When mine packed-up it also put a slow drain on (and thus flattened) the battery — which would not show up if you have (likely) a cut-off switch. If you have current on that wire when the key is off, change the regulator.
Good luck!
Mark
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