The P-Rails Wiring Bible, Part 2
In the previous part of this article, we saw that the P-Rails pickup can be thought of as two separate pickups, like this:
This does of course mean that we can completely ignore one of the pickups and wire the other in as if it was a single coil. However, it’s unlikely that anyone who owned a P-Rails would want to do this.
The three most-used modes for the P-Rails pickup are series humbucker, P-90 mode and rail mode. If these are the only three modes we want to use, the wiring is quite simple. We can do it by using standard humbucker wiring and coil splitting. Firstly we connect the green and bare to ground. Secondly, we connect the black to hot. These connections will never change for any of these three sounds.
We can also solder the red and white together, as we’ll never need them to be unconnected. This combined red and white wire is now what controls our three modes.
Firstly, it can be connected to nothing else at all. This means that the pickup is wired as follows:
The path from ground to hot goes through the rail, then through the P-90, and finally out to hot. Both pickups have been combined in series, so this gives us our series humbucker sound.
Another option is to ground the red and white wires, while leaving them connected to each other. When this happens, both sides of the rail coil (green and red) are connected to ground, meaning the rail is taken out of the equation completely and can be ignored. The pickup is now wired like this:
The white wire is of course also grounded, meaning the P-90 coil is now acting as a regular single coil pickup on its own. This gives us the P-90 mode.
Finally, we can connect the red and white wires to the hot output of the pickup (the black wire). This means the pickup is now wired like this:
By connecting the red wire to the hot output, we’re allowing the signal from the rail coil to become part of the signal. However, by connecting the white wire, we are shorting out the P-90 side of the pickup and it will not be heard. This gives us our rail mode wiring.
To go between these three modes, the simplest trick is to use a 3-position on/off/on DPDT switch, wired as follows:
You can see that you only need one side of the switch, meaning you could control two separate P-Rails pickups with the same switch.
Of course, you can change around the positions of the wires to have the different modes activated in different positions of the switch. Or you can use your own switching system – perhaps wiring the pickup into a super switch, or using several push/pull pots to achieve the desired effect. The purpose of this article is to give you the understanding to decide on your own wiring, rather than just shoving a load of diagrams under your nose with the promise that they all work, but we’re not going to tell you why.
There’s one more kind of wiring that you may want to use with a P-Rail: both coils in parallel. This means that the green and white wires are grounded, and the red and black are connected to hot, like this:
Now we really are just treating the two sides of the P-Rails as two pickups that just both happen to be connected into our signal, much like when the two pickups on a Tele are both active.
Clearly this means we can no longer just solder the red and white wires together. The green is still grounded and the black is still hot, but our switching system needs to take into account that the red and white wires may be separated, with the white being grounded and the red going to hot. This requires different switching – for example, you can use an on/off/on DPDT switch to achieve series/P-90/parallel modes like this:
However, this sacrifices the rail mode.
In the next and final part of this article, we’ll talk through some common wiring systems for the P-Rails pickups. Hopefully you’ll either find the one that’s best for you, or create your own that gives you exactly what you need.