While restoring my factory radio dept with a oem harness, I disconnected a medium size orange wire. About 18" long ,it has a in line fuse and what appears to be a black plastic box inline also. What is it?

 

Sounds like a constant +12 volt wire with an inline fuse. While most after market radio harnesses have the yellow wire as constant +12v, some others are different. I take it you are replacing an aftermarket deck with a stock one, right?

 

I thought that big square box was a noise filter ......

 

oops!!! should I have left that on there??:lala:

 

My bad, yes, niose filter. As long as you dont have any noise, no problem.