Re: Installing a tachometer on an old Evinrude.
If you can't find a gray wire in the control box or the wire bundle from the motor, find the gray wire on the engine that runs from the terminal block on the starboard side of the powerhead, to the plug. Disconnect that wire and then do a continuity check between it and the wires at the other end of the wire bundle, until you find that correct one.
If the wire bundle is a stock OMC item, you should find a gray wire in it, but sometimes exposed wiring fades, gets coated with dirt, grease etc. The above should help you overcome that, but I recommend marking the wire once you have located it. Electronics stores sell identifcation tags/sleeves with numbers and letters on them, or you can just find some gray electrical tape and wrap a piece around the wire.
Also, your tach will probably have internal lighting, so don't forget to run a hot lead from the switched side of either your instrument lighting switch or the running light switch, to the post on the back of the tach for internal lighting.
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