I have several old school mallory and vintage sunco tach which I would like to put onto my 2006 Street Bob. I know I need to have then switched over to a 2cyl mode from the 8 they are now but was just wondering, what wire on the bike will be the output for the tach? Seeing how the bob;s didnt have a tach (???) and I'd like to put one on it. Thanks for any help guys.