95 Cavalier interior lights and radio go out accel or braking?

My son a couple of states away has a 95 Cavalier 2 door, 2.3 liter C24. He says when braking the power doors, interior and panel lights and radio go
off when braking. There is a CLICK CLICK then they go off. Apparently they come back on when in steady state (no brake or accel). He also said this sometimes happens under rapid acceleration though there is no click.
I think he tried pulling the codes but the guy said there was too many?
Since I am not a GM man I know little about these autos. Is there anywhere he should start looking? Voltage regulator/alternator?
He has a voltmeter, I told him to check the power to the radio with the voltmeter while driving to see what the voltage was doing (power and ground wires to the radio).
Am at a loss. Any hints would be appreciated. Will let you know any followup results. Thanks.
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I would start by checking the battery voltage when charging then check all the body grounds on the electrical system. Getting a service manual with the wiring diagram would help in troubleshooting. Make sure all battery connections are clean and tight.

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