Your light has been on for that long? Yeah, its time to read those codes. Your '85 and my '86 are nearly identical, you have the EEC-IV computer system. The emissions light came on because some component part of the system malfunctioned. When I bought my truck, the EGR valve pipe was so clogged that it would usually kill when idling for more than 5 minutes or so. As for the code reader, I am about to buy one. I have not had any luck getting the codes to show using a multimeter.
I would suggest you get a copy of the Haynes manual for the Bronco, it has really good info on the whole emissions system in general, why some of the components fail and how to troubleshoot them. Read the sections 3 or 4 times, they seem confusing at first but start to make sense as you read them again. Also, get under the hood and actually look at what is being described in the book - it makes things so much clearer.
Let me know how it goes, and if I find something really interesting, I'll be sure to post it.