Step 3: Checking PhaseFor the next step, you need to set your DMM to the 2 volts DC (direct current) setting, or if you have auto range, simply to DC. On certain DMMs, you also have to connect your probes or cables to the volts input for this test. Consult your DMM manual.
If you built the polarity testing unit from one of the recent Mod Garage columns, it will work for this step as well. To learn more, read “Build a Pickup Phase Tester, Part 1.”
Note: If you have an analog meter with a needle, be careful with this step—you don’t want to destroy the needle when it’s moving backward. If possible, adjust your needle somewhere in the middle of the scale.
Connect your probes to two of the wires that belong to the same coil. In this case, I picked the green and red pair. I clipped the red probe to the green wire and the black probe to the red wire.
Now take a screwdriver, or any other piece of iron, and place it against one of the poles on one of the coils. Then remove the screwdriver and notice how the reading on your DMM goes positive and then negative—or vice versa—before returning to zero. It’s important to resolutely tap the poles and remove the screwdriver quickly. Otherwise the reading won’t be very clear.
Tip: To protect the humbucker, place a thin piece of cotton, like an old t-shirt, over the pickup so the screwdriver doesn’t directly touch the pickup. The thin fabric won’t influence the reading.
What we want is the reading that first registers positive when you tap the poles with the screwdriver, and then goes negative when you pull the screwdriver away from the pickup. This tells us that the two wires are in phase on this specific coil. If you’re getting a negative reading first, reverse the two probes and try again.
I was lucky with the test pickup—I got a positive reading when I first touched the poles and a negative reading when removing the screwdriver. This tells us that the green wire (connected to the DMM’s red probe) is the start of this coil, and the red wire (connected to the black probe) is the finish.
Next we’ll determine which coil corresponds to the wire pair that’s currently connected to the DMM. For this, perform the screwdriver test on each coil. You’ll notice that one coil will yield a much stronger reading than the other. In our case, the top coil produced a reading of 0.15, while the bottom coil only registered 0.019, so it’s clear that the green and red wires belong to the top coil.
Step 4: Checking Magnetic PolarityIn our last step, you need either a pickup magnetic polarity tester or a simple small analog compass with a needle. (We dedicated a previous column to the topic of pickup polarity; click here if you want to brush up on the details.) A funny story about that column: Some weeks ago, a reader contacted me saying the compass trick I covered wasn’t working with his pickups. After exchanging emails, it became apparent that for this test the reader was using his iPhone set to compass mode. I had to inform him that, regrettably, he’d need a real compass to complete the test. (Alas, few humbuckers are currently capable of sending GPS data. But who knows? It might be a good marketing gimmick.)
Anyway, at this point we want to determine the top coil’s polarity. That’s easy—simply touch the coil with the pickup magnetic polarity tester or your compass (not your smartphone) to see if it has a north or south polarity. In our test humbucker, the top coil’s polarity was north.
Okay, we’ve been working with one pair of wires (the red and green pair on our test humbucker), but now it’s time to turn our attention to the second pair of wires that belong to the other coil (blue and yellow, in this case). Clip your DMM to them and do the screwdriver tap test described above.
Because one of the coils in a humbucker has a reversed polarity, this time we’re looking for a negative reading first. I got that initial negative reading with the red probe connected to the blue wire and the black probe connected to the yellow wire (Photo 3), which meant that in this coil, the blue wire is the start and yellow is the finish. The bottom coil also gave a stronger reading in the screwdriver test, confirming that it’s connected to these two wires. Finally, repeat the polarity test on this coil (again using your tester or a compass). In our case, voilà! The bottom coil had south polarity.
Whoo—you’re done! To master this operation, you’ll need some humbuckers to analyze and a bit of practice, but it’s worth the time and effort to learn this simple technique, because you’ll gain a much better understanding of how a humbucker works. And, of course, you’ll be able to reverse-engineer a generic humbucker’s color-code scheme.
In closing, Photo 4 shows the internal connections inside our test humbucker, clearly revealing what goes where. Normally you can’t see these connections, even with the metal cover removed, so a big shout-out to my friend Michael from the LeoSounds pickup company for custom-winding the humbucker I used to demonstrate the procedures in this column.
Next month, we’ll dive into another guitar mod by analyzing what Fender did to add some silence to a split humbucker on their Select Carved Top Jazzmaster. Until then ... keep on modding!