Question Replacing Coil w/ External Resistor Label

ta400man

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Mar 22, 2006
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Engine Info: 1987 Mercruiser, 165HP, 3.7L, 224CI<br /><br />I want to replace the coil for preventative manitance. When I recieved the coil I noticed that the coil stated "Use when external resistor".<br /><br />I reviewed the schematic for the engine and noticed there is wire that run between the positive side of the primary function of the coil and terminates at the electric choke. I am making the assumption that this wire is in place to allow current to be dumped onto the choke and protect the coil. This wire is also labeled as a resistive wire.<br /><br />Is the resistive wire running from the coil to the electric choke the External Resistor the Coil References?<br /><br />Thanks In Advance,<br />Shawn
 

ron7000

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Jul 10, 2004
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Re: Question Replacing Coil w/ External Resistor Label

your assumption that current is dumped is incorrect. Without going into technical stuff about electricity, the wire from the coil simply feeds the choke with power so it will operate. From the sound of it, you have a breaker-points ignition. I'm not familiar with that year/model so others who hopefully have access to that engine diagram will advise you better. With your coil + terminal, it should be wired such that current coming from your ignition switch when in the run position, will go through either a "resistor wire" or a "ballast resistor" before getting to the + terminal at the coil. This is so that a slightly lower voltage, and current, flows through the breaker points and they live a longer life. I don't know the history of the boat, so current can be routed many ways from your ignition switch before it gets to your coil + side, like the choke, and still be correct so unless you are good with electricity/electronics and can figure it out, you'll need the correct diagram and trace wires. Or if you can post your diagram I might be able to explain it.
 

Fishermark

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Re: Question Replacing Coil w/ External Resistor Label

Is the resistive wire running from the coil to the electric choke the External Resistor the Coil References?<br />
Yes.<br /><br />Although... the flow is not from the coil to the choke, but the other way around. And, as I understand it, if your wiring is like mine, the 12v + wire actually splits before the choke - with full 12v to the choke and then the other wire spliced into the resistance wire which leads to the coil.
 

ta400man

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Mar 22, 2006
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Re: Question Replacing Coil w/ External Resistor Label

Thanks Guys.<br /><br />I will try to post the schematic that I believe to be accurate on Monday. I will check the routing of the wires and match the harness up to the schematic.<br /><br />Thanks,<br />Shawn
 
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