If you're reading this webpage, then you're probably the type of person who likes to rewire, swap pickups, and generally "mod" your own guitar. Unfortunately, there's no "standard" wiring codes or colors in guitar pickups, so its only a matter of time before you have a pickup in front of you with unknown wire colors coming out of it. Here I present a simple way to determine both the function, and the phase, of any guitar pickup. As a side benefit, you should also have a reasonable idea of the pickup's identity and character.
I use Seymour Duncan as my "standard" for several reasons, but mainly, they're my favorite pickup manufacturer and they also provide a wide variety of wiring diagrams. If you can equate any pickup's wire colors and phase to a Seymour Duncan pickup, you can easily wire up just about anything.
This is how a standard Seymour Duncan pickup is configured:
Notice that I've made no mention of "start" or "finish" of the coil, or the the coil wind direction. I've also made no mention of magnet polarity. Thats because they aren't relevant to what we're doing here. You don't need to know any of those things in order to be able to install a variety of different pickups into one guitar, and know that they'll all be in-phase with each other and wired correctly.
Its always dangerous to make assumptions, but at this point, I'm going to assume two things: One, you have a meter, and two, the "bare" wire of the pickup is chassis ground. That is, its soldered directly to the metal frame of the pickup and has no connection to the coils. (We will come back later and discuss 2-conductor shielded cables.)
Note: For what we will be doing, and for all guitar wiring duties in general, a pair of test leads with the small "clips", or "grabbers", are indispensable. Its not a good idea to make any measurements while holding the meter leads with your fingers. Your fingers will have a certain amount of resistance that will skew your readings, and more importantly, we need to be doing other things while the leads are connected. Get a pair of clips when you get your meter. You'll thank me later.
We will also need to have a basic screwdriver. A #2 Phillips is ideal. (A #2 is the size thats approximately 1/4" in diameter.) Anything will work, but we need a little metal. A very small screwdriver will simply make meter readings harder to see. Its also better not to have a magnetized screwdriver, and wrapping the metal with something soft would be good too. Its not much of a problem with most humbuckers, but certain humbuckers, like the Seymour Duncan Stag Mag, and most singles, use magnets for the pole-pieces. During our test we will be bringing the screwdriver up against those poles and we don't want to risk chipping the brittle magnets.
First, neatly separate the individual wires of the pickup. Strip just enough insulation off each end so that you can make a good meter connection, and if there's an outer sheath, strip enough of it back so that you can clearly see the individual wire colors. Like this:
Put your meter on "ohms", or resistance. If it isn't an auto-ranging meter, start at around the 20k range. If you don't have that range, go to the next range higher. Connect the black meter lead to any one of the four leads. Doesn't matter which one. Now take the red lead, and connect it, one at a time, to each of the other leads until you get a reading. Generally, your reading should be somewhere between 2k and 20k ohms. Write down on a piece of paper the color of the two wires you're connected to and the meter reading. Don't worry about which is connected to the red meter lead or black meter lead at this time. Its fairly safe to assume now that the "other" two wires are the other coil. Connect the meter leads to them, and note the meter reading, anyway. Hopefully, both coils will have had a similar meter reading and they'll both be in the "normal" coil range as stated above.
Note: Some pickups are designed with mismatched coils, and some individuals make their own "hybrid" pickups from two different humbuckers. Don't be concerned with a resistance mismatch as long as the general range is in the area stated above. Just make a note of the mismatch.
At this point, you should have a piece of paper something like this:
Now that we know which wires go together, we want to determine which wires go to which coil. Place the meter on its lowest DC volts range. Connect the meter leads to either pair of wires that we know go together. It doesn't matter which color meter lead on which wire at this point. Now bring the screwdriver up against the pole pieces, and then yank it away. Like this:
Leave the meter leads where they are and do the same to the other coil. You may wnat to go back and forth two or three times. One coil will consistently generate higher voltages than the other. Thats the coil that your meter leads are connected to. Note on your paper, (stud or screw), which coil had the stronger readings. Now move the meter leads to the other two wires and repeat the test. Hopefully, the "other" coil will now generate the stronger readings. If everything has gone correctly so far, you now know which wires go to which coils. Your paper will look something like this:
The only thing we don't know now is absolute polarity. To determine this, we're simply going to repeat the test we just did, but we'll be watching the meter a little closer.
Note: It will probably occur to you that the step we're about to perform could have been done at the same time with the previous step. That is correct, and after you've done this once or twice, that will be your natural procedure. I wanted to list them as separate steps just so you'ld be sure to note the different things we're looking for in each step.
Again, with the meter leads connected to one set of wires, (and you know which coil you're connected to), bring the screwdriver up against the pole pieces . . . then yank it away. Notice that as you bring it toward the poles, and then yank it away, the meter will indicate a positive voltage in one direction and a negative voltage the other. (On digital meters, you'll see a "minus" sign to indicate a negative voltage.) If the meter reads negative as you approach the poles, and positive as you yank the screwdriver away, reverse the meter leads on the coil wires. Repeat the test. Hopefully, you'll now see a positive voltage as you approach the poles, and a negative voltage as you yank the screwdriver away. The red meter lead now points to the positive coil wire and the black lead points to the negative coil wire. Note this on your paper.
Repeat that test for the "other" two wires. Again, note your findings on the paper.
If everything has gone as planned, you'll now have a piece of paper that looks like this . . .
. . . and you can transpose those findings onto a Duncan sketch. Like this:
Now you know everything you need to know to connect this pickup into any guitar and have it in phase with any other pickup from any other manufacterer. Or, to be more precise, any other Seymour Duncan pickup, or any other pickup that you've performed this simple procedure on.
Note: I know this seems like it was a long read, but once you've done this once or twice, you'll realize that the whole procedure takes a minute or two. Thats a lot less time, and frustration, than getting your new pickup installed, and realizing that its out-of-phase, or operating on just one coil . . . or not operating at all.
One last note. Remember, in the first paragraph, I said there were some side benefits? While many websites, forums, and manufacturers poo-poo the idea of equating DC resistance to sonic qualities, its a simple fact that a correlation can be made between the two. Of course you won't know exactly what a pickup will sound like, and there will always be exceptions, but when you add your two coil readings together, you can get a reasonable ballpark idea of what your pickup's character will be. A pickup that reads in the 6.5k to 8.5k range will be somewhat vintage PAF-ish. A humbucker that reads 14k or more will probably be pretty "hot" with an attenuated high-frequency range. Its just a "ballpark". Enjoy.