Magneto wiring 1956 Johnson 25hp RDE-17

[osaga]

I'm trying to wire up a magneto rebuild on my 1956 Johnson Seahorse RDE-17 25hp electric start and I can't remember where all the wires go...

Magneto plate has the following going into it's underside: (2) spark plug wires. (1) vacuum cut-off switch wire. (2) wires leading from the hot side of the starter motor.

I believe the following:
Condenser wire goes to the points assembly.
Spark plug wires go to the screw-in post connector on the coils (duh).
Vacuum cut-off switch wire goes to one points assembly.

Not so sure:
Coils have two wires, one goes onto a mounting screw/ground, and the other to the points assembly. (is that correct?)
The two wires from the hot side of the starter motor, that come up through the bottom of the mag plate, connect to each point assembly. (really?)

My logic on those last two: I'm guessing that when the starter button is pressed, some electricity is routed to the breaker assembly in order to pre-charge the condensers with 12VDC. Is that assumption correct? Wouldn't that also momentarily put 12V dc through the coil to ground? and wouldn't that potentially fry the coils?


Any help would be greatly appreciated. The lake is calling.

 

[oldboat1]

Might help some: http://www.fiberglassics.com/library/images/a/a7/Evinrudeservice002.pdf

 

[hardwater fisherman]

I am pretty sure no voltage goes to anything under the flywheel..

 

[racerone]

Stop-----Do not apply 12 volts to the breaker points !!-----The 2 wires going to the points are connected together to STOP the engine.

 

[osaga]

Ok, The two wires leading from the hot side of the starter motor, up through the bottom of the magneto plate, shouldn't be attached to the points. That makes sense because when the starter is engaged, I'd be putting 12v to ground not only thorough the coil, but also through the points contact to ground. Phew.

So does anyone know where those two wires go? I could just delete them but they're definitely original to the motor, or at least attached prior to 1982. The motor ran pretty well recently, magneto re-build was spurred due to loosing spark on one cylinder.

 

[racerone]

The 2 wires are routed to the front of the boat.-----Connected together with a button or ignition switch.-----That stops the motor.

 

[F_R]

The '56 did not come from the factory with any kind of stop switch. Somebody must have added them. If so, they lead to the stop switch..NOT to the starter!!!

 

[F_R]

BTW,, a RD-17 is a 1955 motor, not '56. Same wiring though. But you say the magneto was rebuilt. Whoever did that work might have swapped in a 1958 or newer mag. That would account for the stop wires. Nevertheless, they go to a stop switch, not to the starter.

 

[osaga]

Thanks for the replies. It is the RD-17 Motor so it's a 1955, my mistake. (the boat was built in 1956)

It has it's original remote controls with push buttons for start & choke at the helm, along with throttle and forward/reverse. No kill or ignition switch. To stop the motor I pull the throttle all the way down to it's lowest position.

The two wires through the bottom of the magneto that I keep harping about I'm pretty sure are connected to the large hot post terminal on the starter. That is the post that also connects the starter via a big thick wire to the starter solenoid. I'll double check this because it has been mentioned that it makes a lot more sense for it to be connected to a kill switch.

 

[osaga]

After another look at the two wires coming through the bottom of the mag plate, they are indeed connected to the large hot terminal post on the starter motor. The only logical explanation I can come to regarding these wires is that they were an attempt by someone in the distant past to create a better ground connection for the two coils in the magneto. Meaning that one side of each coil was connected to these wires, and the other side of the coils were connected to the points assembly.

Surprisingly there is some continuity to ground at the hot terminal on the starter motor when not enguaged. This would explain why the motor ran pretty well despite the coils being only grounded to through these wires.

Lastly, I can find no kill-switch on this motor, only a vacuum cut-off switch which acts to shut down one cylinder under certain conditions, and what appears to be a mercury switch mounted to a throttle cam which acts to prevent the starter from engaging at higher throttle positions.

So unless anyone can tell me why 12V would have been supplied to the magneto only when the starter is engaged, my plan is to eliminate these two wires, and ground the coils to the mag plate itself, as is tradition.

Also, if any of this made sense to you, congrats on your degree of knowledge and reading comprehension.

 

[racerone]

????-----The 2 sets of points are only grounded together when you want to STOP the motor.-----They should not be grounded at any other time !!!

 

[F_R]

I think we've made it pretty clear that the wires are for stopping the motor, and should not be connected to the starter. And also that they are not original to a 1957. And yes as you said, the 1957 did not have any sort of a kill switch. So proceed with your plan to just remove or disconnect the wires. Leave everything else alone.

BTW, the continuity to ground at the starter terminal is the resistance of the coils within the starter. No surprise.

I consider this case closed now.

 

[racerone]

Perhaps just another example of how wires and voltage and amps are difficult to understand at times.-----Case closed here too.

 

[osaga]

Thanks for trouble shooting this with me. The case is nearing completion but I have a couple more questions....

I ordered some new Johnson/Evinrude OEM coils which arrived today (part# 0584477). One of the two wire leads is shorter than the other. The short one is black and the long one is green. It would be easiest to connect the green wire to the points rather than the ground screw, as it is longer. And to connect the black wire to ground, as it is shorter. Would there be any difference with regards to which wire connects to ground?

Lastly, I noticed that the magneto plate attaches to the engine via a greased brass swivel coupler to the to of the engine. Does that ever cause a lack of ground continuity to the block as the grease may insulate the magneto plate?

Thanks again

 

[racerone]

Well the long one goes to the breaker points.----The short one goes to ground.------And some overthinking on your part about grounding / insulating by the grease !!

 

[F_R]

Wire coming off the TOP of the coil is ground wire. Wire coming off the BOTTOM of the coil is points wire. Even if you are color blind. And yes it does make a difference if you get them backwards.

The only electricity passing through the mounting junction is spark voltage returning back to coil. Being on the order of 10,000 volts or more, it has no trouble getting through the grease. Besides, it is to be greased very sparingly.

 

[osaga]

Bizarrely, the short top wire is black, and the long bottom wire green.

Here’s a link to the coils I purchased.

https://www.ebay.com/i/260746033982

I’ll go go ahead and disregard the wire color. Thanks again.

 

[oldboat1]

black short wire attaches to the top of a coil mounting screw. Long green wire.goes to points. Make sure wires do not hit spinning flywheel (tuck them in). Laminated edges of coils must be mounted absolutely flush with the flat machined areas of the mounting posts (sets the proper magnet air gap).

 

[osaga]

Thanks for the mounting tips. I'm sure it's a simple procedure for most but to the uninitiated it is confusing, grateful for the help.


Here are some part numbers in case it's helpful to anyone coil shopping in the future:

Evinrude Johnson OMC Coil 0584477 is equivalent to parts:

• 18-5181 Sierra Marine
• 777659 Evinrude Johnson OMC BRP
• JE-C100 OBR Red Rhino
• 9-23102 Mallory Marine
• 72100 GLM
• 183-4477 CDI Electronics

Which fit the following Johnson and Evinrude outboards:

• 1.5 / 2 / Junior 1968-1990
• 3 / 4hp 1950-1976 & 4hp 1981-1989
• 5 / 5.5 / 6hp 1950-1976
• 7.5hp 1954-1958
• 9.5hp 1964-1973
• 10hp 1949-1963
• 15 / 18 / 20 / 25hp 1951-1972
• 28 / 30 / 33 / 35hp 1956-1970
• 40hp 1960-1973

 

[racerone]

Some of us have years and years of experience on these simple motors.----But thanks for the coaching in post # 19.