What year?
It really doesn't matter, you probably fried the CVU (Constant Voltage Unit) aka CVR (Constant Voltage Regulator) mounted on the back of the cluster. It's not much bigger than the end of your thumb. It turns the 12vdc signal into a 5vdc signal, which is what the gauges are designed to run on. If it goes bad, you either have no voltage to the gauges, or too much, which may fry the gauges as well. The tach, if you have one, may still work even though the CVU is fried.
Take care
~Chris
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Retired Moderator
MustangNet
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JimPorterRacing
RACECAR spelled backwards is RACECAR
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