Wiring diagrams for merc Tach

[iwanttofish]

Does anyone have any diagrams on wiring a tach for a merc 115hp I bought one and it has the 5 plug harness but when plugged in it did nothing. There is a light brown wire that is not hooked to anything. The tach is not mounted either so I was not sure about grounding the unit had anything to do with it. :shrug:

Thanks in advance for any infomation.

Mike