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The 'pink' resistor wire

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Original Curbster

Joined: 22 Jun 2005
Age: 57
Posts: 8071
Location: TX, USA

1969 Mercury Cougar XR7

PostPosted: Tue Dec 06, 2016 5:43 pm    Post subject:  The 'pink' resistor wire Reply with quote

In the picture below we see a typical Ford ignition circuit. The voltage comes from the ignition switch through the 'pink' resistor wire to the positive (also called the + or ign) side of the coil.

<center><img src=""></img></center>

<b>But what is that 'pink' resistor wire doing there?</b>
The purpose of that wire is to reduce the voltage going into the coil from full battery voltage down to roughly 9 volts.

<b>Why would you want to do this?</b>
Because the coil is optimized to work at 8 or 9 volts.

<b>Why do this when the car has a 12V battery and the charging system puts out ~14 volts when running?</b>
So you will have 'full' voltage to the coil during start-up. If the coil was optimized to run at 12 or 13 volts it would deliver a very weak spark at start-up due to the considerable draw from the starter spinning the engine. Make 9V the "normal" operating voltage for the coil and it will be happy all the time.<i>
Here's another thing to consider: Have you ever had your alternator fail at night? Your lights are getting dimmer & dimmer but the engine is still running normally. Why? Because the coil doesn't care what the charging system is doing as long as it's getting it's 8 or 9 volts. Drop the voltage too low and you will get misfires and eventually the ignition shuts down.</i>
So now the engine is running and the charging system is putting out 14+ volts. Without the ballast wire the coil would be getting almost double it's optimized voltage. This will lead to an overheated coil and reduce it's life considerably.

<b>So I need the pink wire?</b>

<b>What about the 12V 'performance' coils?</b>
If your coil says it uses a 12V feed chances are it is internally ballasted. It is expecting 12V in and then reducing it internally. GM used this style in the 50 and 60s. Ford and Mopar used external ballasts; Ford used the wire and Mopar used a ceramic ballast resistor like this one:
<center><img src=""></img></center>
In fact, all of the 'performance' coils that I have seen come with an external ballast resistor. You don't want to use a coil that requires 12V in with a Ford ignition circuit. You will only have 9V going into a coil that is going to reduce the voltage further with an internal resistor. The 'performance' will be disappointing to say the least.

<b>Why will the engine fire with a broken/bad pink wire?</b>
The starting circuit has a 'bypass' wire that delivers full voltage to the coil when the key is in the 'start' position. This voltage comes from the "I" post of the solenoid. When the solenoid is engaged the I post is energized with full battery voltage <b>after</b> the ballast wire and tach. Once the key is released to the 'run' position the solenoid disengages the bypass line voltage drops to zero and the resistor wire delivers the voltage to the coil. The beauty of this design is that you get quick starts AND long life for the components.
<i>Note: You will have 9V at the I post of the solenoid when the key is on because the bypass wire is being back-fed from the coil feed.</i>

<b>Can I tap into the pink wire?</b>
No. The pink wire is an integral part of the ignition circuit. It's length determines it's resistance so you should not cut one. You can tap into the circuit either before or after the pink wire, but should avoid tapping into it.

So now you know WHY we have that annoying pink wire stealing that power giving voltage from our coils. Hopefully I have explained this in a way that makes sense.
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