External Resistor

Just got new coil today. On the side of the coil it says "use with external resistor." What is meant by this? I have a 1989 OMC 5.0.

Re: External Resistor

As long as you haven't modified your ignition system, you already have the external resistor.

Why are you replacing this coil?

Re: External Resistor

the external ballist resistor cuts down the voltage at coil .. check to see if the one that was on the boat had one ... also check the voltage on the hot side of coil with the key in the on position if its 12 volt the boat probably doesnt have an external ballast resister . when i replaced the coil in the one i am working on i took readings dor both the low side ohm resistance and the high side and matched the new coil by doing that .... low side is checked across the positive and negative post of the coil in the 20 ohm range then the high side is tested from either post to the center coil wire post in the 20k ohm range ... hope this helps

Re: External Resistor

chaparall villain 2 said:

also check the voltage on the hot side of coil with the key in the on position if its 12 volt the boat probably doesnt have an external ballast resister .

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Not quite correct. It will read 12 volts with or without a ballast resistor if the points are open but much lower with the points closed if there is a ballast resistor present.

Re: External Resistor

Everything posted above sounds right. I'll just add a brief explanation of the purpose of a ballast resistor. Speaking roughly from days of owning a 67 Barracuda;
The purpose of the ballast resistor is a design point to allow higher coil output when you start the engine. The ballast resistor is in the circuit while the engine is running. It reduces the coil voltage to a moderate level. (10V?) When you start an engine the resistor is bypassed and you have the full 12V at the coil thus giving you a greater output. Probably need a scope if you want to observe this in action.
In my experience (60s & 70s) I have seen them on Chrysler products. Even so, I thought external ballast resistors disappeared when electronic ignitions arrived.
If a ballast resistor fails (open circuit) the engine will start (on the 12V bypass) but then die as soon as you disengage the starter circuit (no more voltage to the coil). The quick fix was to jumper out the ballast and drive home with 12V to the coil.