Re: 1975 Evinrude 70hp Tech Install
If you have the OEM manual, it should have a color wiring diagram in the back. Additionally, in the "ignition" section, there is a figure with a diagram of the terminal board on the motor where the gray wire will connect to (gray wire is your tach signal wire).
If you open your remote control, you should find a gray wire tucked away in there. That is your tach signal wire. Tach power should wire to the purple wire terminal on your key switch, ground to ground in the remote control, gray signal wire to your signal input on your tach. There may be a wiring harness kit, but my tach did not have it so I simply opened the remote, did all the wiring there with short leads and spade connectors, and reinstalled the remote. I then made connector wires from the tach to the short leads, again using spade connectors. That way, if I need to remove the remote control or the tachometer for any reason, I don't have to have dangling wiring or disassemble the remote control.
The manual does actually discuss connecting a Tachometer very briefly in the Remote Control section of the OEM manual. Its under the heading "Accessory Connections" and basically it says to refer to the instructions in the Tachometer Kit. It does, however, say that the Tachometer should be the only instrument wired to the remote control. All other accessories should be wired directly to the battery.
Hope that helps
Rgds
Eric
