Just replaced battery and check engine light is on

[70-k5]

Search function isn't working tonight, hopefully somebody can help me with my issue.

I was playing with the PA-12 trying to get it working. I had the key on for 20 minutes maybe a half hour. Then the radio stops playing. I think great, I fried it with this new input. I try to start and I get a click and a loud beep similar to locking the doors but louder. I realize that my sister probably never changed the battery so in I go.

Battery out - to the store to get one. Costco doesn't carry them. Stop at Napa and they want over $200. End up at Batteries Plus and they have one for $125 - $10 instant rebate and -$10 mail in rebate. Get home, stick it in and I'm live again. I get the PA-12 to work, awesome!

I decide to clean the engine cover, then get to the side covers. While I have them out I figure since I've got the covers off I'd change the spark plugs I picked up last week.

Yes I have ADD, and I'm focused, tearing things up.

Get the plugs changed, put everything back together and go for a test drive.... somethings wrong, check engine light is on and feels like I'm missing a cylinder.

Get home and find #5, passenger side front plug electrical connection was just a hair from locking in. I lock it in, take it for test drive number 2 and it feels great. More responsive, throttle just feels lighter. Unfortunately the check engine light is still on.

I'm familar with OBD1 engine management systems, I'm assuming that this vehicle is a little beyond sticking a paperclip in a port and watching a light flash... How do I clear the light?

Oh, and I hope I didn't give too much information, I didn't want to be vague....