'69 Evinrude 115983E wiring questions

I have been trying to trouble shoot some issues with my motor. I removed the cover to the terminal block to check the connections for loose or broken wires. In the number 7 spot there was a wire that was loose and missing the screw. It is Gray and Black and said that it goes to the amplifier. I replaced the screw and tightened it back in place. The wire that was disconnected goes to the Safety Circuit Ignition Assembly. From there I am not sure. Is there any reason why this wire would have been disconnected and would it cause a lack of power at WOT? The motor does run without it being in place but will not hit WOT under a load. What does the amplifier do and what does it look like?

Second issue, is tach related. My tachometer is disconnected and the wires were cut at the gauge. On the wiring harness/cluster that comes from the motor to the ignition switch there are several wires that are cut and not connected to anything. Is the wire for the tachometer in this group of wiring and if so which one is it? I read somewhere else on the forum that the wire is gray. There is a gray wire in this group of wires that is cut.

Does anyone have a color coded detailed layout of what each of the wires goes to that is in the wiring harness that is at the ignition switch? I would like to try and get everything reconnected and back in operating condition. At present time I have no gauges what so ever that work. There is a fuel, tach, speedo, and volt gauge in the dash. The fuel gauge I am not worried about because I have a remote tank with a built in sight gauge. I would however like to at the very least have a tach.

I appreciate the help in advance.

Re: '69 Evinrude 115983E wiring questions

Since this boat is quite old, it is highly likely someone has mucked with the wiring so the way it was when new is probably not what it should be today. Since ALL of your gauges are inoperative it is highly probable that +12 volts and/or ground are missing when the key is in the RUN position. Gauges are powered by the "A" (accessory) terminal on the ignition switch. The big red wire in the engine to helm harness is the main +12 volt feed. That wire connects to the "B" (battery) terminal on the switch. "S" is the starter/solenoid terminal and is hot when the key is in the START position. There should be two "M" terminals on the switch. Those two terminals are connected by the ignition switch when it is in the OFF position. That shorts the ignition to ground to kill the engine. There is also a fuse at the engine. That fuse protects the wire harness. If it is blown or missing, you get no power to the helm, hence no instruments or starter function. The voltmeter only needs +12 volts and ground to function. The speedometer is not electric except for the light. It works off the pitot at the back of the boat. The tach, fuel gauge, and trim gauges all have sender signals. So they need +12 volts, ground, and the sender signal to operate. The tach is the gray wire in the engine harness. Fuel gauge sender is pink.

Re: '69 Evinrude 115983E wiring questions

The ignition switch I replaced myself because the old one was worn so bad that the key would fall out. I replaced it with the same switch that was already in place. It has a bat, ign/sol, and one other terminal. If I am following you correctly then, that extra post is the one that needs to have the wires run to the gauges, correct? I will have to go take a look at the switch again to figure out which wires go to where. As far as the rest of the wiring. The wires in the harness just go from the motor to there and are cut that are not connected to anything else. The rest of the wiring is brand new that powers my switches, graph, radio and pumps. I replaced all of that myself and just ran two 10 gauge wires from the battery to the circuit breaker/switch panel.

My tach only has three wires running to it. One says ground, one is signal and the other is for the light. Where am I supposed to hook the power wire at that is for the 12v?