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74 70 horse ignition wire IDing

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R F

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I bought a new ignition switch for my 74 70 horse. I have identified the Bat wire, the ground wire, the solenoid wire, and the choke wire. I still need to determine which of the last two wires is the magneto and the other would be the ignition. I may be in luck as one of the two wires is yellow and black--a yellow and black wire comes out of the harness in the motor and runs to a 12 block wire housing-to block #6----and that block states yellow and black! So if anyone can tell me if that is the magneto or ignition, I can ID the last wire by elimination. PS the last wire is all light blue. Thanks.
 
The ignition on this motor does NOT use 12 volts to make the spark !!!-----Magneto kill wires go to the M terminals.-----Do not hook up anything untill you are sure what happens when you turn the key !!
 
It was assumed that the magneto wire is a kill switch-but is it the blue wire or the yellow and black wire?
 
Blue wire???

One of the two "M" terminals on the back of the ignition switch is normally a raised (tower like) terminal... the black/yellow wire attaches to that terminal

The other wire should be plain black and attaches to the regular looking remaining "M" terminal.

The ignition is self powered (Magneto Capacitance Discharge)... battery voltage would destroy it!

With the key OFF... the "M" terminals are connected internally, effectively grounding out the ignition circuit.

With the key ON or in START position... the "M" terminals are NOT connected and the ignition is engaged.

Same theory as a push type kill button.
 
It was assumed that the magneto was a ground to kill system. Also now that you have ID the black/yellow I now know what all 6 of my wires are-thank you. And yes the blue wire, I have 6 wires that run to the switch one is all blue. The old switch had BMMSC&A the new BMMSC&I -----I assume that A stands for ignition accessories (power tilt, lights ect) and that I on the new switch is also ignition accessories. The blue wire is the one that hooks up to that terminal as I can positively ID all the terminals and wires and thanks to all--but if any of you are concerned that I'm making a mistake please save me.
 
The 1974 40hp has the beloved Lo Tension Magneto. Only used a few years. I think you have the wrong wiring harness (?)

 

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R F said:
It was assumed that the magneto was a ground to kill system. Also now that you have ID the black/yellow I now know what all 6 of my wires are-thank you. And yes the blue wire, I have 6 wires that run to the switch one is all blue. The old switch had BMMSC&A the new BMMSC&I -----I assume that A stands for ignition accessories (power tilt, lights ect) and that I on the new switch is also ignition accessories. The blue wire is the one that hooks up to that terminal as I can positively ID all the terminals and wires and thanks to all--but if any of you are concerned that I'm making a mistake please save me.
Click to expand...

Ah yes... it had slipped my mind that model incorporated the blue wires.
 
Yes things are working! I almost lost it because the screws that attach the terminals can touch in places that are "out of sight" I got smoke on turning the key, but then I found that two screws were touching in back-thought I toasted something but I was quick enough-that was close! Then the choke worked without pressing in on the key- another case of screws touching. Bent some tabs-fired up on the first try-ran better than before:eek::eek::eek:. Thanks to all
 
One last thing---that smoking--could I have blown the battery recharging and not know it yet? How do I test that the mags are recharging the battery and the voltage regulator is okay?
 
I guess I screwed that one up! Somewhere, my twisted brain got the idea we are talking about a 40hp here. Obviously, my previous reply is not valid. Sorry.

To see if your battery is charging, clip a voltmeter on it and check the voltage before starting the motor, and again after it runs awhile. Voltage will increase a bit when it is running if it is charging.
 
fdrgator said:
I guess I screwed that one up! Somewhere, my twisted brain got the idea we are talking about a 40hp here. Obviously, my previous reply is not valid. Sorry.
Click to expand...

Yeah... That lead me astray also (the blue wire thing)... On the 1974 70hp There shouldn't be a blue wire leading from the engine wiring harness. That should be a black/yellow wire to the raised tower like "M" terminal and a black wire from the other "M" terminal to ground.

Funny... I studied both of those wiring diagrams, read their description... never gave it a thought, never dawned on me. Make one hellava detective huh? :)

This "blue" wire... where does that lead from... and to?
 
The blue wire starts at the switch on the A or I terminal (I is the Seirra knock off symbol) It becomes hot from the battery when the switch is turned to the run position. The wire may have had a second color that sun faded. I think that it may not run to the motor but comes off the harness before the motor-when a charge is put to it it draws no current. When the blue wire is not connected the motor runs perfectly. When the blue wire is connected the motor runs perfectly. I think it is for lights, horns, power tilt that kind of stuff- my harness has a spot two feet from the motor were several wires use to run out of the harness but have been cut and capped with tape. The wire may have been purple and faded or purple blue
 
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R F said:
The blue wire starts at the switch on the A or I terminal (I is the Seirra knock off symbol) It becomes hot from the battery when the switch is turned to the run position. The wire may have had a second color that sun faded. I think that it may not run to the motor but comes off the harness before the motor-when a charge is put to it it draws no current. When the blue wire is not connected the motor runs perfectly. When the blue wire is connected the motor runs perfectly. I think it is for lights, horns, power tilt that kind of stuff- my harness has a spot two feet from the motor were several wires use to run out of the harness but have been cut and capped with tape. The wire may have been purple and faded or purple blue
Click to expand...

Yes, any wire attached to either a "I" or "A" terminal of a ignition switch (in your case, the blue wire) would have 12v applied to it, usually for accessories. Your speedy response which clears up the confusion on my part is much appreciated.
 
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