SR S14 bogs down at night

[bilik]

Hey guys, been having this issue on and off for a while but it's starting to get pretty bad. Car runs fine during the day time, but once I turn my lights on for night driving it pegs the AFRs full rich to 10.0 and sputters the entire time. My current guess is alternator but I'd like to know if anyone has seen this and might know a simpler fix. Thanks!

Possibly important info: 95 S14, 98 SR, SAFC, Optima yellow top battery (newish)