No spark in stihl 025 chainsaw. I replaced the

Check the ground wire on the on and off switch, it could be a bad ground

Where did you get the coil? How did you gap the coil? Reply below please.

This tests the entire system:
Ignition Coil Test by SmallEng.com
http://www.youtube.com/watch?v=L7WNBDRG4C4
You may need to use a jumper wire between the threaded part of the plug and the cooling fins. You do not have to bend up the electrode.

Ignition module gap
Place a business or index card between the fly wheel and coil, rotate until the magnetic attraction pulls everything tight together. Tighten the coil screws, rotate the flywheel until the attraction eases and remove the card. Ensure nothing contacts when flywheel is rotated.

If you have more questions or need additional help please reply below and I will get back to you. Thank you for using FixYa and Good Luck. HTH
Lou