Try this link. I had a similar problem. The GDL website is good cause it shows you how to test all the cruise parts. Before I went through the tests on the gdl website I actually called the guy, described the issue, and they virtually assured me it was the amp. Told me not to even bother testing the other stuff. Popped in a used amp and problem solved.
http://www.peachparts.com/shopforum/showthread.php?p=883130#post883130