Ballast Resistor or not?

[YOBE]

Mercruiser 6cyl in-line 165HP 1970's-80's

I have checked all my spark plugs for spark and have been able to start my engine for the first time, very short as cooling was not active yet.
Afterwards I did some electrical work and discovered that on the positive side of the coil I only have around 9.5V. Seems weird as I thought this should be 12V.
But then I found out that sometimes a "ballast resistor" is used to drop the voltage and protect the coil. But I have no clue where that resistor could be located... Can not be that small....
First impression is that the 12V from the ignition key cable directly flows to the coil.

My next step is to measure where I create the voltage drop (perhaps ignition key itself...)
My question: is there another way to be sure if a ballast resistor is required? Do not want to destroy the coil by testing it directly to 12V.

Thanks Yorick

 

[Scott Danforth]

You should have 12 volts only when cranking.

The ~9 volts is so you do not burn the points up when running. You have a resistance wire in your engine harness vs a ballast resistor

 

[YOBE]

Oh... I'm learning something new now.
So when I switch on the ignition key and provide power to the coil it is normal to measure around 9V? This thanks to a resistance wire.
But when turning the key towards cranking I should see 12v. Is that the reason why I see 2 brown wires at the coil? Didn't make sense to me why 2...

I will measure once during cranking!!! I wonder.
And sorry for these questions, but someone really "messed around" with the engine and cabling so I do not trust anything anymore. I want to get as close as possible to original condition.

Remark: also the interrupt switch (from the gear change) is removed. Probably broken. But to my understanding it should normally pull the other side of the coil (-) to ground. Right?

 

[Candy Gramformongo]

The resistance wire sold as a repair part (84-94227A2) is a pinkish-purple insulated, thin, stiff wire about three feet long. Look for it as the last part of one of the wires going to the coil, though I suppose it could be anywhere.

In working on my boat of the same era as yours, I just assume all wiring is suspect and restore everything having to do with what I am working on. Many times it is easiest just to wire around the original wiring with a new wire.

 

[Scott06]

Oh... I'm learning something new now.
So when I switch on the ignition key and provide power to the coil it is normal to measure around 9V? This thanks to a resistance wire.
But when turning the key towards cranking I should see 12v. Is that the reason why I see 2 brown wires at the coil? Didn't make sense to me why 2...

I will measure once during cranking!!! I wonder.
And sorry for these questions, but someone really "messed around" with the engine and cabling so I do not trust anything anymore. I want to get as close as possible to original condition.

Remark: also the interrupt switch (from the gear change) is removed. Probably broken. But to my understanding it should normally pull the other side of the coil (-) to ground. Right?

If the points have not been replaced with pertronix etc then yes this is correct. During crank voltage drops a bit anyways, normal on points ignition to bypass the resistor for hotter spark and quicker starting.

yes the shift interrupt grounds the negative side of the coil to momentarily kill the spark. This is only when coming out of gear. The engagement teeth on the dog clutch has a 5 degree back cut so unless the drag from the water on the prop is briefly unloaded, it wont come out of gear. As the shift cable wears or corrosion puts drag on the shift linkage, the shift interrupt will trip going into gear. So if someone took it off it is likely due to having shifting issues .

if the harness is hacked up you likely can find a good used harness on ebay.

 

[Bondo]

Oh... I'm learning something new now.
So when I switch on the ignition key and provide power to the coil it is normal to measure around 9V? This thanks to a resistance wire.
But when turning the key towards cranking I should see 12v. Is that the reason why I see 2 brown wires at the coil? Didn't make sense to me why 2...

I will measure once during cranking!!! I wonder.
And sorry for these questions, but someone really "messed around" with the engine and cabling so I do not trust anything anymore. I want to get as close as possible to original condition.

Remark: also the interrupt switch (from the gear change) is removed. Probably broken. But to my understanding it should normally pull the other side of the coil (-) to ground. Right?

Ayuh,..... I donno the wire colors, but when you turn the key to "start", the slave solenoid powers the starter's solenoid, which powers the starter, 'n the outside tiny terminal of the starter's solenoid, which sends battery voltage to the points, only when starting,.....

 

[ROY WILLIAMS]

The key starter engine on , coil 12 volts of the ignition coil + ...
The ignition coil run engine , of the resistance 1.8 wire, key on engine on 9 volts ignition on .