Wiring Up A Teleflex Tach

[KQQLCAT]

First let say I am new to the boating world. I bought a 20' pontoon with a 2005 Mercury 60ELPT Big Foot EFI and the toon has no gauges. I think that I have the wrong prop on it and I am told that I need to install atach to determine this.
So I bought a Teleflex tachometer. Went to install it and what I thought would be simple is not so much. Diagram is not much help. The wire I need to get to is in the remote control and wiring seems a little tight in there. If I take this thing apart is it going to explode into pieces? Looks like it will. Is there a diagram on how to take this apart?
Thanks for any help.
Pat

[Silvertip]

The control box for a 2005 Merc should have a three terminal plug right below the key switch. Buy the tach harness. Plug it in and go. If you look at the wiring around the control box you should also find a "gray" wire with nothing attached. That's the sense wire for the tach. No need to get inside the box. There should also be a +12 volt and ground wire in that same bundle.

[KQQLCAT]

I did buy that harness but to my surprise there was no plug on the control. My telflex wiring instructions tell me to connect to the yellow but merc says gray. Here is the wiring diagram attach.tachwire.jpg