12 volt coil

Bruce,
What's the coil for? I can't answer you part number question but I'm sure curious! I know different coils with different resistances are used with or without the ballast resistors but that's typical when you are doing a ignition system mod. What happened to the original ballast resistor? Put one back in and use the standard coil????? More info!!!

Bruce,
OMG!!!! Yup, young guys behind the computer at Napa! I only hope the had preliminary training at Autozone! Sorry!!

OK, you do have or do not have a ballast resistor on the 100? Considering it's age, you should have one! Confirm the volts you get to the coil.

Riley wrote: Pete, It does not have one and the manual states that engines with alternators do not have them, so apparently they weren't used. Volts to the coil? That would be on the + side?

Yes, but be sure about the manual and the voltage - you know how things where always mixed up back then!!! I still say you should have a nominal 9 going to that coil. Which engine is this?

Pete, it's the 100, 6 cyl. I'll test the wire going to the coil and see what it reads. I'm finding coils on line. I was just surprised it was not an easy purchase this morning at NAPA. But, now that I'm finding some on line, the question is what resistance is the engine supposed to have? The manual does not say.

Sweet, there was one older guy there that knew what I was talking about. He told the kid he would have to read the specs of each coil in the computer. He said 20 years ago he would have known the number. Sound familiar?

They are easy enough to find on line. Don't know why the auto parts stores can't come up with one easy. The old Interceptor parts manual list it as well. This appears to be it.
http://pertronix.carshopinc.com/product_info.php/products_id/116621/40511

Bri892001 wrote: What do these ballast resistors actually do? I realize they are the norm on most of our boats but I don't get why. It sees like the resistor is lowering the voltage, just to have the coil up it again before it goes to the distributor?

The purpose of a ballast resistor is to lower the voltage on the primary side of the ignition circuit. This reduces the wear on the trigger mechanism. Distributors equipped with points will usually require them, else you stand to wear them out prematurely. Electronic distributors with optical sensors tend to require ballast resistors as well. Most magnetic pick up style allow you to eliminate the resistor and run the sensor on a full 12V. The lowered input voltage at the coil does not significantly reduce its output voltage (30kV+), which is what is sent through the cap and to the spark plugs.

Marinizers handled the need to drop the voltage at the points differently. Some, like PCM, used big ballast resistors installed on the motor. Others used in-line resistors (resistive wires). Others used resistive coils (which is what Bruce is looking for). All do the same thing (knock the voltage down at the points). You just dont want to use more than one method at a time, or you stand to lower the voltage too much, which causes no-spark or weak spark conditions. When swapping out to electronic ignition, you also need to follow the distributor/module's manufacturer's recommendation on supply voltage.

Tim, where were you all weekend? I could have used your help. Pete, a tractor web site had the most info on it and got me sorted out. I was surpised to find that Interceptor was using internal resistance on their engines so far back. If you have an alternator on your Dunphy, it shouldn't have an external resistor, although one could have been added. I've got just under 12 volts at the battery and 11 volts at the coil, so I need the linked coil.

Good info and story, Marty. I knew this wasn't spposed to be so complicated.

Thanks, makes a little more sense now.
I read this: http://www.jetav8r.com/Vision/Ignition/CDI.html so that helped a little too.

Pete, it's in the wiring diagram. Those marineengine.com manuals are not all they're cracked up to be, especially for the price. I've bought 2 of them and the middle 70 pages is the same filler stuff on both of them. They advertise to make you think you're getting this great Interceptor shop manual, but they've been cobbled together with a collection of the guy's stuff.