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Why do they use both 6 and 12 volt in the ignition system??

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Wingryder

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Helping a friend replace the starter selenoid on a old 1975 inboard/outboard with a 302 Ford engine. Not used to seeing both 6 volt and 12 volts in the same system. The Voltage is dropped via a giant ballast resister that gets pretty hot doing its job.

The voltage from the key switch to the selenoid was 6 volts big as life. That kind of threw me a curve. The boat owner said something about it is 6 volts until the engine starts and then goes to 12. What???

Please explain

wingryder
 
I'm not aware of any dual voltage required for a Ford Marine starter motor.

Ditch the old Ford style Bendix drive starter motor.........



............ and replace it with one of today's HTGR/PMGR technology starter motors.
Cost will be about the same.





This will kick a$$ over the Bendix drive unit.


.
 
I agree with Hystat..... the 16 ga purple/black wire is the "start-by-pass" circuit.
As he says, this provides a full 12 v during cranking ONLY.
Once the starter motor drops out of the loop, the coil receives resisted voltage.


Back in 1975, this would have been a Bendix drive motor for the Ford Marine engines.
This schematic would be correct if the starter motor had been replaced with a solenoid kickout style starter motor.

If you go with a HTGR/PMGR motor, then by all means use this schematic.

73_OMC_V8_all_big.jpg
 
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It was a simple replace of the starter selenold. Engine cranks fine now. But when you measure the voltage on the "ignition" pole of the selenoid (coming from the key) It is indeed 6 volt. Stays six all the time. the "start" pole goes to 12 volt when key is in crank position as it should but that six volts still throws me. I would think bad ground or bad key switch. But 12 is coming from that very key switch to kick the starter selenoid in.
I think there is more to this story.

wingryder
 
Follow the purple ignition wire and the purple/black wire.
The purple wire powers the IN side of the ballast resistor.
The purple/black wire is on the OUT side of the ballast resistor, and connects to the By-Pass circuit point of origin.
Where the purple/black wire connects to the point of origin, take a voltage reading with the + side of the ignition coil disconnected.

You'll be coming at this in a reverse fashion, but I believe that this should show you the resisted voltage.
 
judging by the report of how huge the ballast resistor is, I would guess someone replaced the original with some generic automotive part that is too high of a resistance. 6V might be enough to make a functional spark, but spec. is generally 9V minimum on OMC

and they do get hot - give you a good burn if you touch one when it has been running for a while
 
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