Heaven only knows what led me into my thermostat replacement (it was sitting around waiting for me so I digressed) when the real issue for me was WIRING. As I’ve already posted, having some intermittent issues with my solenoid fusible link (I think) and needed to fight through the under hood spaghetti to try to find the weak spot (sort of ongoing). Meanwhile, while chasing everything that runs across the front of the vehicle (under the upper rad support) all of which was found to be relative to 1) trickle charger and 2) MSD box. As I moved through and chased each wire down I thought it odd that the orange lead off the MSD was connected to the coil (-) post and the black lead was connected to the coil (+) post. Finding that to be counter intuitive I looked up the schematic and found the reverse to be correct (as presumed). BUT, I found in the data abyss we call WEB that reversing the two is a “known racing/performance hack” to retard or advance timing without unbolting the distributor. Not sure I understand the principle unless one is switching back and forth to meet emissions and then to run the scalded dog, er cat. At any rate, popped the timing light on and confirmed my previous 14 - 15 degree idle advance and rolled it back to TDC. Then I switched the wires. I then reset myself to about 15 degrees (didn’t bother checking total at this time because my timing light was fagging on me; it is almost as old as the car). Noticeable difference. I never really had an issue with the way the car was running, it wasn’t a beast, but I got my thrills with it - but NOW, I have to moderate pressure on the throttle from a stand still if I want to save rubber. Very interesting, but not sure I know why. 15 degrees is 15 degrees; isn’t it?
Not necessarily if the electronic ignition was miswired! Nice find - congrats!
I’m surprised that it ran. I may be wrong but reverse polarity at the coil might have reversed the direction of the spark. Is that even possible? I vaguely recall something called the right hand rule.
It appears you are “spot on” with reversing spark direction; I guess it makes sense, but I question the need to “spare voltage” with an MSD system - there’s more than enough to go around. MSD obviously does not approve of the “hack”, and you would think they would tell you how to best “optimize” the system. According to Google AI (automotive ignition?): AI Overview
Reversing the polarity in an MSD (Multiple Spark Discharge) system—swapping the orange and black wires to the coil—is done to ensure the spark jumps from the spark plug’s hot center electrode to the cooler ground strap, which requires up to 30% less voltage to ionize the air-fuel mixture. [1, 2, 3, 4]
The Core Principles
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Thermionic Emission (Hot Electrons): It is physically easier to pull electrons away from a hot surface than a cold one. Because the center electrode of a spark plug runs significantly hotter than the threaded ground strap, making the center electrode negative allows electrons to flow more easily. [1, 2, 3, 4]
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Voltage Demand: If coil polarity is reversed (center electrode is positive), the ignition requires more peak voltage to create a spark, causing premature wear on the ignition components and increasing the risk of misfires under high compression or heavy loads. [1, 2, 3]
How an MSD System Works Differently
Unlike standard inductive ignitions that step up 12V, MSD boxes use Capacitive Discharge (CD) technology. They dump 450 to 500+ volts into the coil’s primary winding. Because of how these units are designed, the MSD output inherently produces a negative high-voltage spike at the coil tower. [1, 2, 3, 4, 5]
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The Orange Wire acts as the primary positive trigger.
Reversing these primary coil wires inverts the magnetic field inside the coil, shifting the secondary output polarity. This allows you to calibrate the system so the spark plug fires with the correct negative polarity. [1, 2, 3, 4]
Troubleshooting Pickup vs. Coil Polarity
It’s important not to confuse coil polarity with magnetic pickup (distributor) polarity. Reversing magnetic pickup wires (the violet and green wires) is used to dial in your base ignition timing rather than for spark efficiency. [1, 2, 3, 4]
AI is pulling together what it finds on the internet - and some of it might be true. That is an interesting concept about applying negative high voltage to the spark plug tip. Could be some truth to that.
The electromagnetic field around the coil will collapse to produce voltage in the direction to keep current flowing the same direction as when the primary was energized (according to the right hand rule). So the polarity of the spark would indeed be reversed by reversing the primary current flow through the coil.
But I am doubtful that reversing the magnetic sensor leads is a better way to set your base timing than just rotating the distributor.
I’ve forgotten more than I ever knew.
I’m afraid it’s all a bit too technical for me; but these are the only things I trust AI for - giving the “average return” of data. I wouldn’t bank on it either, and at the very least your last comment sums it up “just rotate the distributor”.
That’s what I hate about this station of life; relearning what I’ve forgotten and then forgetting it again.