Rider,
It could be the sail switch or the fan motor itself, or even the blade binding up. There has to be air flow detected by the sail switch for the lighting cycle to complete. You probably have a Suburban furnace like I do in my Tour Master -- most models are covered in the on-line manual you can find here:
http://www.bdub.net/manuals/Suburban_Service_Manual.pdf
There is a pretty good troubleshooting section in this 40 page manual...let us know what you find and if you need additional things to look for.
Chuck