I've got a 99 civic dx, and I recently lost the key, so i replaced the ignition cylinder and key with one out of a 98 ex civic.
The new key works fine, but ever since I put the cylinder in, the series of 4 beeps continues when the door is open, with the key out of the ignition.
And my headlights are not on. If anyone's got any ideas please let me know. I know I could remove the beeping alarm entirely but I would like the warning when my lights are on and keys are out.
Upon finding the old key and putting its cylinder back in the car, this all still happens.
Let me know, Thanks.

 

Check whether the ignition key switch closes when you insert the key.

C415 = 7P connector that you unplugged to replace the ignition switch

1) Disconnect battery connectors.
2) Disconnect the C415 connector.
3) Insert key into ignition.
4) Use multimeter to test for continuity between pin 2 and pin 4 in female side of C415 connector.
5) You should detect continuity. If not, the ignition switch taken from the 98 Civic is bad or the Blu/Wht wire(s) is broken.

 

I had the same issue after I changed the cylinder in my 95. I'm not sure if there the same but on mine there's a leaver sticking up the slides into a slot on the lock. Mine was stuck so I just disabled it.