1987 Mercury 25 hp run/stop switch & plug wires wiring questions

[seanymph85]

I had recently purchased this 1985 Sea Nymph boat with the above mentioned 1987 25 hp Mercury outboard. I was having trouble with the start/Off switch not shutting the motor off. Shortly after I discovered what I thought was just a loose black wire seemingly under a silver plate with 4 phillips head screws. I soon discovered this wire from the stop switch was just laying there loose under the plate and was not fastened to anything at all. I am attaching a picture to illustrate which wire was not connected to anything. I did a continuity test on the switch with it in the off position and found no problem with the continuity in that position. There was no result from attempting to test continuity with the switch in the run position but the motor started with the switch in the run position.
In any case I need to know if anybody knows where the single black only wire is supposed to be attached to.


Also hopefully it is okay to ask a second unrelated electrical question in this post. If not please let me know and I will post it separately. I noticed some "crud" around the spark plug wires where they go into the "coils". I tried to pull them out but there was apparently considerable build up on the ends where the fit into the coil as they would not come out. When I finally got one out the wire had come out of the connector and I had to pull what was remaining out of the "socket" with needle nose pliers. Two questions: Can the end of the wire be reconnected to the snap in connector that goes inside the coil and still work properly and what can I use to clean the crud out of "socket" in the "coil" that the end of the wire goes into? Can any kind of spray be used to help? Is there some kind of small round wire brush that can be used? My battery cable wire brush is to big for this.

 

[bilge rat jim]

Re: 1987 Mercury 25 hp run/stop switch & plug wires wiring questions

1. Your switch- the wire with the bullet connector should plug in to the stop circuit wiring harness (black/yellow), and the other attaches to a ground point on the engine block
2. Yes you can probably get away with re-attaching the connector to the plug wire- just shorten the plug wire 3/8" to make sure of a good connection. I use some rolled up emery cloth to clean the contact on the coil, and then blow it out with compressed air.

 

[seanymph85]

Re: 1987 Mercury 25 hp run/stop switch & plug wires wiring questions

1. Your switch- the wire with the bullet connector should plug in to the stop circuit wiring harness (black/yellow), and the other attaches to a ground point on the engine block
2. Yes you can probably get away with re-attaching the connector to the plug wire- just shorten the plug wire 3/8" to make sure of a good connection. I use some rolled up emery cloth to clean the contact on the coil, and then blow it out with compressed air.

Thanks for this information! I believe the silver plate that has the 4 phillips; screws I mentioned contacts the block of the motor near the back end of the motor at the base or lower section of the cowls area. There is a matching silver plate with 4 phillips screws (perhaps aluminum plate) on the opposite side of the motor otherwise in the same area. In any case I believe it contacts the motor block on the end of the motor where the cowls release is located and would work as a ground point. Otherwise I will see if the wire will reach to any obvious ground points on the block. Do you know if the continuity test on the switch would come out that way if the switch is working properly? Showing open circuit in the run position and closed or continuity in the off position.

Great idea on the emery cloth. I can roll it up to just the right size and still be able to turn it to clean the connection. I need to know if I need to strip a bit of insulation off the end of the plug wire so there can be a short piece of center wire/fiber to fold under and contact the end connector/clip at some point. I have an air compressor with nozzle to blow it out afterwards. This will just be temporary as I am looking for new plug wires. If anyone has input on a quality brand or type that conducts the spark/voltage really well and holds up I will appreciate your suggestions. Or if any of the auto parts stores etc. that sells them as some things for motors from marinas are often far more expensive for the same thing. Also I assume it is okay to use some type of electrical grease on the coil end of the plug wire to help prevent corrosion etc. so the plug wire will come out next time like it's supposed to. Any particular brand or type suggeested?

In the middle of difficulty lies opportunity Albert Einstein

 

[bilge rat jim]

Re: 1987 Mercury 25 hp run/stop switch & plug wires wiring questions

Yes, one of the screws on the cover plate will work as ground. Best to use a soldered-on ring terminal, and a star washer to maintain contact. And yes, if the switch is disconnected from the stop circuit, you can test it as you described.
When you are installing the terminal on the plug wire, strip it back about 1/2", and fold the wire back on the insulation so it makes contact with the tang on the terminal. I would not advise using dielectric grease or any other goop on the connection, even dielectric grease offers some resistance. The only time you should ever have to remove it is if a coil fails, and then, if you're as smart as I think you are, you would probably replace the plug wire anyway.