More on Coils

Dear Mr. Motorhead:

Thank you so much for your explanation on coils. However, in your last article, you said that you were not going to get into the explanation of coils with built-in or external resistance. I know for myself, I would like to have a complete understanding of all this cool stuff. So, what’s it all about.
Signed, Alfie

Dear Alfie:
You are so correct. My apologies for not giving you the complete story. Here is all the stuff as you have requested. Our old boats were first equipped with 6 volt electrical systems, as most old boaters know. The coil in a boat that remains 6 volt has no resistor either built-in or external. So from now, on you have one less thing to be confused about. Just go to your local auto parts store and by yourself a 6 volt coil and install it as I suggested before.
Many of us have decided to convert our old boats from 6 to 12 volt systems. Now, we have a different scenario. Hang onto your hat, because here is the really cool stuff.

Remember, the coil makes mega-volts that is sent to the right spark plug via the distributor. Inside your distributor is a set of contact points. The points are like a switch; they turn the mega-voltage on and off at precisely the correct time allowing the spark to do its deal. With your newly- installed 12 volt system, you are sending twice as much voltage across these points. The end result: they wear out and or get fouled up much faster. The solution is to reduce the voltage that goes through your points back to 6 volts. This is where Mr. Resistor comes in. Actually, for the technically inclined, a ballast resistor. The built-in resistor-type coil looks just like the original 6 volt model. It does all the neat things I just talked about, but no one knows the difference when they are inspecting your engine. This is for those of you who prefer the perfection side of the coin. The downside to this type of coil is the increased cost. Some say they also have a potential to wear out faster and not work quite as well. I can only comment on the cost issue, and this is true.

The external resistor is just that. It is a separate piece of electrical gear, you install between the (+) terminal on your coil and your ignition wire. The resistor is a small white porcelain contraption about the size of a disposable lighter. You can mount this on the bracket that holds your coil to the engine block. The down side here, all the judges know you have converted your boat to a 12 volt system. If you want to go this route, ask the parts guy for a ballast resistor that would be installed in a 55-57 Chevy. The choice is yours. I recommend that you shop at parts stores such as NAPA. The do-it-yourself auto parts stores (Champion) will look at you like you have two heads when you ask them about this stuff.

One side note: When your coil is failing, it may not just quit right away. Your engine will run very poorly as if something else might be wrong. Put your hand on the coil. If it is very hot, that is your problem. One method to get you home, assuming you have a cooler on board, ice her down to keep it cool and your engine running.

Mr. Motorhead