Rough ride

I love my 1987 Nissan 300zx. she’s not a turbo but frankly she doesn’t have to be to make me happy. my problem is this: she runs real rough recently. when i turn on the AC, it gets worse, and when i give it gas, the AC seems to lose power. also, it appears that certain types of electrical drain (e.g. lights on ) seem to affect this condition (though not always) i’m at a loss at the moment to figure it out. i’ve got new plugs and wires on it, so i’ve ruled that out… but i’m just. . at a loss. anyone got any ideas?