Have wires in back seat what is the blue wire

[mntlimg]

Bought used base model Bronco. I bought it after they had owned it 2 1/2 months. They must have added an amp and. Pulled it out before trading it in. I have a kicker ground wire black. A blue wire and a cut speaker wire from woofer cover. Not sure what the blue wire is from and where to look for the other end of the speaker wire?

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[IDyeti]

Typically there is a small gauge blue wire as a power trigger to turn the amp on/off with ignition.

Based on the pics you have though, blue appears to be a 12V positive (hopefully its fused), black is ground. red/black is speaker wire splice, likely to rear the speaker.