wire question...

Hello, my 1991 lerado XJ has a wire coming off the bottom post of my alternator going over to one of the post that holds down my ignition coil...anybody know what that is for? It looks like it has a small amp inline on it to..anybody replaced one of these, and where did you find one?...arty:

What color is the wire?

Thanks 8mud.......I'll get back to you on that, it keeps raining here in Texas...