First, hook the fans up to a 12v source and see if they work. If they do (I'm betting they will), it's probably a wiring issues. You'll have to follow the wires and hopefully it's just a loose connection. Could be a coolant temp sensor or relay as well, but try the simple things first.
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'13 Mustang 3.7V6 - MT82
'00 GP SE (L67 Swap, XP, Headers, 3.25")
'98 GTP, '01 Bonne