There's also a fuse on the immobilizer ifself (under the driver's seat). Have you checked that?

 

Not on mine. I pulled it (quite a PITA!) and there is no fuse, outside or inside. I do not have an alarm system, which may be the distinction.

 

Perhaps open up the key fob and check/clean the transponder pill. Can't think of more things to try at the moment.

 

Re-check your connection at the immobilizer antenna (plastic ring around the key cylinder) and the signal convertor ( black box mounted on the steering lock).. make sure they are properly seated. Wiggle them while trying to start.. Did you have these disconnected while doing your ign switch? Seems likely it's something to do with the ign switch replacement, and these are in the area...

 

I didn't disconnect them during the switch install - at least not knowingly. I will check those. Thanks!