This is the exact piece that I used on my Shovelhead:

http://www.foghollow.com/cgi-bin/catalog_new.pl?fid=988645183.104006&query=Category%3DElectric%26Description%3Drelay%26PartNo%3D%26pagenum%3D1%26cgifunction%3DSearch%26s ubmit%3DSearch&cgifunction=form

Oh, a warning. The included wiring diagram is wrong. I can tell you how to connect it if you decide to get one and the error is not obvious.