If a spark plug wire breaks at the end, or if it fails a resistance check and the fault is found near an end, it's cheap, easy, & quick to repair rather than replace it. Carefully remove the separated terminal from the spark plug and clean out any remaining wire fragments.
Use a common digital multimeter to test each wire's resistance (Ford specifies 7KOhm/ft) from the plug terminal (inside the boot) to the cap terminal (inside the distributor cap).
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