Power steering is a weird beast. Normally, with a hydraulic system, there is less load on the belt when turning the steering wheel, as the fluid is not recirculating through bypass and back to inlet ...On board electronics bog down (a/c blower, interior lights, head lights, etc) when I turn the wheel especially in reverse.
... but we 9th Gen Civics have the even weirder electric power steering. There's more load on the alternator (and ergo more load on the serpentine belt) when turning the wheel.
Let's say you're running at half the amplifier's rated capacity (let's call this a continuous duty cycle?). 600W. At 13.2V, that's 45A.... from a bit of research I'm leaning toward overcharged/damaged alternator, bad battery, or something else that's gonna cost me more than I wanna spend. High output alternator? New battery? Faulty wiring. Grounding out? I don't know where to start testing.
I don't know what the rest of our Civics use for steady state operation (EFI, spark and everything else on the CAN bus), but I'd guess that 35A or so, give or take a few, is not unreasonable.
Add A/C and lights (as well as turning the steering wheel), and you can add more ampere draw.
I'm willing to bet that the stock alternator is only about 100A, and your total load of music, A/C, and lights is way past the continuous duty cycle for the stock alternator.
Stock grounds tend only to be big enough to support the original vehicle electronics, plus other possible electronically supported OEM options. I recently fixed grounds on a Nissan Altima V6 by cleaning up the stock grounds and adding some 6 gauge cable with crimped lugs between a threaded boss on the transaxle and a welded threaded boss on the unibody.A friend suggested the issue could be my battery ground not being a sufficient gauge to handle the additional load ...