Were the terminals on the wrecker 440CCA battery at opposite ends as suggested?
As saids by others a battery with too many CCAs did not kill you cars wiring.
If the old battery had 7 volts after charging, you have several dead cells and battery is stuffed.
Maybe what has happend is that the old stuffed battery was supllying stuff all amps. When you put in the wrecker battery a short in your loom somewhere burnt throught the wiring, which is why it doesn't smoke now?
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