89 Johnson 140 vro not revving

[thebottomfish]

Well I got the misfire taken care of and after that I played with the throttle adjustment(thanks for the advice to mess with that after I got the misfire under control) and got it set up, what looks like, as good as it's going to get.
I found out that my control box has a unused port to wire a tachometer effortlessly...except the plug isn't empty.
I have a white wire coming out of it, hooked up to a circular object in the gunnel where another wire, blue/purple (kind of discolored) comes out of the control box and hooks in as well. That's it no other connections.
Any ideas?