Some basic advice needed

[Starman8]

Just trying to understand the flow of engine wiring because the old boat I purchased has a few connections that look odd. Mine is a 1979 115hp Merc tower 6cyl.

On the web, saw a few diagrams, and funny, 1979 was isolated probably because of a change made that was very different, so I need to ask basic crude questions.

1. Coming from the engine is a heavy gauge red and black to the battery. What is being supplied to the engine, controls, and rest of the electrical system via that ONE connection?

2. The harness exiting the outboard has wires that don't provide power to what?

It seems from the scheme below that the battery hookup for the 1979 also wants to go(start) directly to the controls, then flow elsewhere while other diagrams look the opposite?

3. How is my ignition key and control box getting power?

This all relates to the fact that an old boat I purchased has 2 additional (non-red) wires attached to the positive post. The battery POS has 3 red wires, one to the outboard engine, one for the trim motor, one for the panel, then also has a purple wire and a white with green stripe wire connected also?

Somewhere on the web I saw a color code for Merc that says purple to 12v post. This appears to get juice to the key(IGN) at the controls? There is no purple wire that flows through to the helm area.

My efforts are to avoid blowing up the rig, safety by correcting any faulty shortcuts, which is why I asked if any older model Merc owners have any of these other wires connected DIRECTLY to the battery positive.

then after 1979, the following changes

the images were borrowed from maxrules website...............

Any advice would be helpful, especially from anyone who had/has a 1979.

Thanks

 

[Chris1956]

Re: Some basic advice needed

1979 was the changeover from a battery power CDI ignition to the ADI ignition on the inline six. Wiring harnesses were compatable for both types of ignitions, however, not all wires were used, depending on the ign type. In addition, the colors of the wiring changed after 1979. The old wiring colors are the top picture. Your diaghram is also for an ADI ignition. I presume you have the ADI ignition w/o a distributor? The ADI used an orange ign killer wire, and the distributor ignition used a white wire to power the switchbox with 12VDC.

The PTT wiring was seperate from the engine harness. Those are likely the extra wires you see on the battery, although the trim panel should be powered by the connection to the PTT motor. Maybe the other wires power the dashboard, radios, FF...?

The red wire on the engine has +12VDC on it, and it will cary that voltage to the ign key. On the ADI motors, that power was used to run the choke and starter solenoid, via the grey and yellow wires. The distributor ign motors had a additonal white wire that powered the switchbox, which is not in your diaghram.

 

[Starman8]

Re: Some basic advice needed

Chris, you are shedding light on the matter and it is appreciated.

When I tore the boat down, the FF, VHF and other adds black and reds were isolated, meaning separate runs directly connected to the battery with inlines.

This left the engine red/black, the trim motor red/black, then on the positive side, these 3 wires, red(runs through a 15 amp breaker)/purple/white w/green stripe.

Once I get the helm panel back together with an new Easy switch panel, then I may get a better picture that the red mentioned is my feed to the panel. If the other 2 relate to trim or some other mandatory connection, I will have to use process of elimination. All I can say about the purple and the white w/green stripe is that they don't go to the helm panel.

I also need to know where my helm/panel black ground is by the battery. It is at the panel, but me thinks it was split off. I will know if its fine once I test a newly wired function on the panel.

 

[Chris1956]

Re: Some basic advice needed

The original PTT panel had power(red), up(blue) and down(green) wires. However, since Merc incorporated a trim limit switch, they also needed a purple wire for that.
Pushing the down buttom sent power directly to the PTT motor. Pushing the middle button sent power thru the trim limit switch and then to the PTT motor. If the trim limit switch was open, you needed to push middle and top buttons together to bypass trim limit switch and send power directly to PTT motor.

 

[Starman8]

Re: Some basic advice needed

The original PTT panel had power(red), up(blue) and down(green) wires. However, since Merc incorporated a trim limit switch, they also needed a purple wire for that.
Pushing the down buttom sent power directly to the PTT motor. Pushing the middle button sent power thru the trim limit switch and then to the PTT motor. If the trim limit switch was open, you needed to push middle and top buttons together to bypass trim limit switch and send power directly to PTT motor.

The controls harness incorporates a 3 wire run, consisting of blue, green, and purple and leads to the trim motor I have. I traced this connection visually. Here is a bad picture of this cable at the motor:

So this 3 wire cable runs from the controls to the trim motor. The trim motor also has its own red and black from the motor to the battery. What do think would be powering my control switches, the connection from the battery to the trim motor or the connection from my battery to the engine, then that harness powers them? Sorry for being clueless on this.

That purple wire on the (hot) 3 wire cable mentioned that started all this confusion (see pic below) must be a separate power run to the other purple wire on the picture above to complete the trim limiter?(middle wire)

If thats the case, then the limiter has its own separate run..........OK, makes sense.

Then I need to figure out this white wire in the picture with the green stripe on it. Could it be for the trailer switch?

Then again, the other place I see this white w/green stripe wire is on a harness coming/going to the fuel tank along with a black ground and the pink sender. As I mentioned, the previous owner said the fuel gauge never worked, and I can see why just by comparing how its wired versus the schematic that is on this forum. Wherever that white w/green stripe goes to from that tank run is the intended purpose, and with a hot lead in the same coloring, what was trying to be achieved is another direct hookup of an function.

My control arm only has 2 buttons, up and down, and the trailer is on the control box fore:

Someone did mention white w/ green could be temperature warning horn. Where would one find that apparatus to trace the wire?

 

[Chris1956]

Re: Some basic advice needed

I do not think your motor has a overtemp alarm. Since your PTT controller is a bit different, expect the wiring to be a bit different that I said. The trailer button will bypass the trim limit switch. The up button likely has the trim limit switch wires in series.

The gas tank/gauge wiring is real simple. +12V, fuel level sendor and ground to the gauge. Conect ground and the sender to the tank. The sender goes on the stud on the gauge. Ground can be anywhere, but there is usually a screw or spade terminal on th sender, for the ground wire.

 

[Starman8]

Re: Some basic advice needed

based on your reply, do you still feel the purple wire feeds the PTT switches with 12v+

 

[Chris1956]

Re: Some basic advice needed

Provided you have the old wiring colors, the only purple wire I have ever seen runs from the trim up button to the trim limit switch. The trim limit switch is located in the starboard upper trim cylinder bracket. If you trace the PTT harness from the pump to the switches, you should see two bullet connectors. These run to the trim limit switch.