1977 Johnson 115 HP Tach Installation

[antmidty]

Can someone please help me. I have recently purchased a 17' boat with a 1977 Johnson on it. The original owner had the boat completely operational except the tach was not hooked up. I do not know where on the engine to connect the tach, can anyone help explain where to hook it to the engine?

 

[ezeke]

Re: 1977 Johnson 115 HP Tach Installation

If you have a side mount control you have either a three wire plug at the control, or a a taped gray wire inside the control.

Either way, you take the positive feed with a purple wire from the A post on the ignition switch and the black ground wire from the black wired M post on the ignition switch. The gray sender wire runs from the terminal block at the engine, through the main harness to the control and then is connected to the tachometer.

If you have the more recent control that has the plug below the ignition switch, it will be wired as shown in the diagram at this site:
http://continuouswave.com/whaler/reference/ignitionSwitch.html

The earlier controls are wired as shown in the thumbnail below.

You can add lighting to the gauge by connecting the light to one of the blue wires on another gauge or to your panel light switch.

 

[antmidty]

Re: 1977 Johnson 115 HP Tach Installation

Thanks A Bunch Ezeke.
Just one additional question. I'll take a look when I get home later at it, but if I understand it correctly, the black and purple wire come off the igintion switch, not anywhere off the engine itself. Then the gray wire come off of the engine itself off the 'strip' that has many colored wires coming off of it right? The part I am confused on is when you say through the main harness to the control. I am not sure I can picture where that would be, where is the control located? Does this mean to simple run the gray wire from the engine through the channel where the other wires run so that it will come out under the dash where the gauges are located, or does it have to run to something else first? I am sorry if this is a simple question, but I appreciate your help.

 

[ezeke]

Re: 1977 Johnson 115 HP Tach Installation

No, the gray wire is already in the harness running through it to your remote control. "Remote control" is what OMC called the box at the helm with the throttle, shifter, ignition switch etc.

The gray wire is not connected inside the control to keep voltage away from it, because any voltage applied to the gray wire can seriously damage the entire ignition system, especially the rectifier.

Gauges continue to draw electricity as long as they are on, so they are almost universally wired to the ignition switch so that they are off when the switch is off.