97 Sunfire,runs great until you turn on lights

My daughters 97 Sunfire,2.2 engine,auto trans has a strange problem...it runs great until you turn on the headlights or blower motor. the alt is putting out plenty and I even swapped it out with another just to make sure. can the ECM be a possible link? HELP
Thanks,Troy

probably a ground issue... Start by checking the body ground on the battery tray. Can't rule out the PCM yet, but I sure wouldn't start there

How old is the battery?

about 11 months...it load tested good.

Thanks, I recleaned the grounds today and got better results. I'll most likely change the cable this weekend. Thanks for everyones input.