The mounts shown are 1/8″ thick Brazilian Cherry, sized to cover the holes in a pick guard made for full size humbuckers.
I’ve been rewiring some humbuckers from single-wire plus shield (coax) to four wires plus shield, bringing out both coils separately. Apparently, different pickup manufacturers do it any way they wish, with no industry standard. So I’m proposing one, and offer here a tutorial on how to do it.
First, you have to disassemble the pickup. If it has a brass cover, you may find a large gob of solder or two between the brass base and the metal cover. You will have to get a very thin steel veneer saw, of about 0.010” thickness (at a woodworking store). Using heat to melt the solder might damage the coils or magnet, especially if lead-free solder was used.
Place the saw against the inside edge of the cover and saw down through the gob, changing to the other direction occasionally. When you get down far enough, a little twist with a screwdriver between the cover and the base will break the connection. When you get the cover off, dress the tinned surfaces of the cover and the brass base with a small, fine-toothed flat file, to keep any burrs from interfering with re-assembly.
Most 4-wire cables seem to come with wire jackets colored black, white, green and red. In DC circuits, not 110 VAC, black and green are generally assigned to ground. I propose that black and white be assigned to the coil with the south pole up, and green and red to the coil with the north pole up. The poles can be determined with a common magnetic compass – even the smallest and cheapest ones.
The cable shown here is Alpha 1214C, about $60/100 ft roll. It is a little stiff due to an outer jacket that is over-thick for this purpose, but it will do.
Determining polarity requires an oscilloscope. It can be tested by putting a screwdriver tip on the top pole piece of the coil being tested. When the screwdriver is pulled off sharply, the magnetic field relaxes slightly, and causes a small and short pulse of voltage across the output. It’s similar to the string moving away from the pickup pole. I propose that when the pulse is positive on the scope, the side of the coil connected to the scope probe ground is low (black for S or green for N) and the side of the coil connected to the probe tip is high (white for S or red for N).
The wires coming out of the pickup coils tend to be very small diameter hookup wire with plastic jackets. They may even be magnet wire. It’s not a good idea to unwrap the (black) tape on the coils, unless a layer covers both coils and the connections to the coax are underneath it. There may be four wires coming out, or two with a third going from one coil to the next (series connection).
If there are four wires coming out of the coils, they may be connected to each other and the coax, with the soldered ends covered with small-diameter shrink tubing. In that case, you will have to very carefully pull off the shrink tubing, holding the wires between the connections and the coils to avoid breaking the connections to coil magnet wire. Then unsolder or cut the connections.
If there is a third wire going between the coils, it will be short. You will have to cut it carefully in the middle and strip off about 3/32 of jacket from the ends. Then tin the ends with solder. The former ground and signal wires will likely be longer. They should also be tinned in like manner, but leave them as long as possible.
The cable shield is soldered to the brass base of the coil. Cut the output cable shield wire right where it is soldered to the brass base. At this point it is best to remove the coils and magnet from the brass base. If they are not held together with wax, first melt some beeswax into them to do so. Now you can use a soldering iron to remove the remaining shield connection from the base without heating up the magnet.
Now size the 4-wire cable to the pickup. Strip off the outer jacket (usually plastic) so that the cables will pass through a hole opposite the coil connections, pass under a coil down the length of the pickup, and fold around just to the other side of the pickup. Then make sure by partial reassembly that it will actually fit under a coil. If not, you will not be able to use this approach. You may notice that the coax went into a hole nearest the connections. You can do this if you want, but if the shield solder connection to the base fails, the long arrangement is a little less likely to pull the wires out of the coils and break the magnet wire.
Remove the shield from the 4-wire cable down to the point where it just starts to bend around the pickup coils. Strip about 3/32” of jacket off each black, white, green and red wire and tin the ends. You will notice when tinning any of the wires that the jacket may melt back down the wire a bit. So you only need enough bare to start the tinning.
Before you make any connections, test and mark or record the polarity of the wires coming out of the coils. Note carefully which will connect to the black, white, green and red output wires.
On most coax cables, the shield is soldered to the base on the inside, next to the coils, so that one of the coil wires can be soldered to it. In this case, it is easier to solder the 4-wire shield to the outside of the pickup, on the bottom of the brass base, just where the cable goes into the pickup. Since the four signal wires are likely to rub on the cable hole in the brass, it is best practice to first put some heat shrink tubing over them. If the cable has a separate and bare shield wire, it can be folded back over the heat shrink and brought back outside the pickup for soldering to the brass base. You can solder the shield to the base now.
You may need to snip some off the individual 4-wires to make them fit where the coil wires end. You may notice that the 4-wire cable wires are much larger than the wires coming out of the coils. If so, you will need to bend a small J in the smaller wire and loop it about the larger wire next to the jacket. Then solder the two together.
A little bit of solder will do it. Lower temperature 60%-40% tin-lead rosin core solder of about 1/32” diameter works easiest. If you haven’t done it before, practice a lot on scrap wire. It helps to carry just a tiny amount of solder on the tip, so as to make a good thermal connection with the wires, and then add more solder to make the connection. With practice, a good connection can be made in about a second, without melting any more jacket material.
Snip off any of the larger wire that sticks out of the connection. Cap each soldered connection with a short piece of thin and small-diameter shrink tubing. You can hold the iron close (without touching it) to it to make it shrink. You can melt the open end shut to completely cover the connection. In this case, none of the four (black-white-green-red) signal wires is soldered to the shield at the pickup. That, if any, is left for the switching network or preamp at the pick guard control area.
Before you reassemble the pickup, test the connections by putting the scope leads on the other end of the 4-wire cable and repeating the screwdriver test. If that doesn’t work, figure out what you did wrong and fix it. Then reattach the coils to the brass base, keeping the 4-wire cable under a coil (if you could use the long arrangement).
Now carefully fold the connections into crevices between and under the coils. Everything has to fit within the outline so that the pickup cover (if any) will fit back one and the pickup will fit through the mounting hole in the mounting plate or pick guard. Melt some beeswax onto the connections to hold them. You can do this with a soldering iron that has been turned off, but is still very warm, using the tip to guide the wax drops to the right places. Use your fingers, carefully, to mold the soft wax.
At this point, unless you have a pickup cover, you are done. If you have a brass pickup cover, or any other metal that can take solder, solder a small wire or piece of brass foil to the bottom, inside or outside. This will solder to the brass base to complete the ground connection and provide shielding to the whole coil. Put it back on, carefully. Solder to wire or foil to the brass base, and cement the cover in place by melting beeswax about the edges between the cover and base.
If you did not have a brass or solderable metal cover, having either plastic or wood or non-solderable metal, you will have to decide whether or not to bother wrapping the coil with shielding tape. Brass shim stock of 0.001” or 0.002” will do. It can be cut with fabric scissors, and solders easily. You can get it at machine tool stores. Otherwise, music parts outlets sell copper tape.
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