When I have the lights on & I place the car ( 1999 Firebird)on reverse on 1999 Pontiac Firebird

the alternator voltage drops from 14V. to 12V. It takes about 2 minutes for it to start charging again .I have a new alternator & a new battery.What can be causing this problem.

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1 answer 2 comments
COULD BE A REGULATOR ISSUE IN ALT. WHERE DID YOU PRCHASE R/B ALT
I purchased alternator at Autozone.
THAT COULD BE THE PROBLEM, THEY SELL R/B ALT BUT THERE ALT ONLY HAS THE NECESSARY PARTS REPL THAT TEST BAD NOT EVERYTHING. IT COULD BE A WEAK REGULATOR STILL