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Sorry I don't have any good ideas of the cause of your problem, but I can help clear up some bumper information.
There are no electrical disconnections/connections required of replacing the bumper cover unless your car has the following options, and even then, it's only disconnecting/connecting a wiring harness that's close to the bumper (not near the fuse or relay panel).
Good luck!
You may want to check this harness connection to make sure it is good.
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