MIM : Classic Humbucker Installation

Written by
Logan Tabor
Published on
January 21, 2021 1:29:04 PM PST January 21, 2021 1:29:04 PM PSTst, January 21, 2021 1:29:04 PM PST
Welcome, one and all, to another amazing edition of Mojotone’s Make It Monday series!  Today’s episode is going to fall more under the umbrella of a Mod It Monday, but is critical to our lives as techies all the same.  
Today, we will be taking the Railhammer humbuckers out of my Reverend Bob Balch Signature Guitar and replacing them with Mojotone’s Classic Humbuckers.  I just want to clarify that Reverend makes some incredible guitars and their Railhammer pickups are equally incredible. I'm only changing out these pickups for the sake of this tutorial, and I would never be caught dead speaking ill of the almighty Reverend Guitars.  
The actual process of replacing the pickups alone is not altogether that complicated, but because every company’s wiring standards differ, it may be challenging to understand what's actually going on inside our guitars and what needs to be done in order to make the necessary modifications.  Once we analyze the guitar's innards and gain an understanding of what we are working with, however, the steps involved in the actual pickup replacement are minimal.
Here is a short list of tools and supplies we’ll need for today’s project:
Mojotone Classic Humbuckers (or your choice of replacement pickups)Fresh Set of Guitar StringsSoldering IronSolderScrewdriverWire StrippersMultimeter


Below is a short sound clip of how my guitar sounds before I make the swap.  I am playing with a fresh set of strings (this should make for a fair comparison after the swap has been made), on the normal channel of a Mojotone 5E3 Style Amp Kit, with my Volume at 3 and my Tone at 9.  The sound clip goes from neck to middle to bridge…





Alrighty, here we go!  Before we start working on the electronics, let’s go ahead and remove the strings from our guitar, as this will make the removal of the old pickups -- along with the installation of the new pickups -- much easier, and will require us to use fewer swear words throughout the process…




Next, before we loosen our pickup mounting screws and remove the pickups from the guitar, let’s open our guitar’s control cavity using our screwdriver and take a look at what’s going on under the hood (Image 1A).





We’ve got our control cavities open. Now we should be looking at something along the lines of Image 2A below…





As I said before, every manufacturer will have different wiring conventions (i.e., using different color wires for different purposes), and will likely also have different ways of wiring the guitar’s electronics altogether.  Personally, I enjoy my guitar’s current functionality so I’m not going to alter any of the actual wiring or how the components interact with one another, I’m only going to be replacing the pickups. If you wish to also make changes to the way your electronics function, you’ll potentially need to consult your guitar manufacturer, or even scour the internet for the wiring scheme you want (we will cover alternative wiring techniques in future articles).  
Right now, it’s time to take a closer look at everything and start decoding our guitar’s wiring scheme.  In my guitar, and this will be the case with many humbucker guitars, the pickups are using 4-conductor wiring, which means each pickup has 4 leads that need to eventually have a “home.”  These leads should be black, red, green, and white. Additionally there should be a bare wire lead. In Image 3A below, you’ll see my hands holding two thicker black wires; these are the pickup leads, and the black housing is actually just the insulation for the smaller internal leads.  


Note : In the above Image you’ll notice each of the green leads are soldered to a lug on the pickup selector switch.  This is actually an indication that Reverend is using their green wire as the hot wire for the pickups.


Mojotone’s wiring convention is to use the black wire as the hot wire (these will be soldered to their respective lugs on the pickup selector switch) and to use the green wire as the ground connection.  This ground connection is being made to the metal casing of the pickup selector switch -- our green ground wires along with the bare wire (shield wire) should be connected to this ground point.
But there is still the issue of the red and white leads for each pickup.  For this application, the red and white wires from each pickup will actually get twisted together, soldered, and then covered in a non-conductive insulator such as electrical tape.  Take a look at Image 4A below to see what Reverend has done...


Note : I have removed the non-conductive insulator from one set of red and white wires to show what is happening underneath the insulation.
IMPORTANT : Take pictures of your control cavity and make as many notes as necessary before removing the old pickups.  This way, we’ll have information to reference when we go to put our new pickups in. In my case, I need to make a clear note that I will be reversing the function of the black and green wires when I go to install my new pickups.  


In my wiring scheme, all of my pickup lead connections are made right here at the pickup selector switch.  And because I’m not changing the function of the rest of the electronics, this is all I need to focus on.  So for now, let’s get our soldering irons hot and prepare to remove our pickup leads from their current soldering points.  Once your iron is hot, heat up the joint that contains each lead and remove the leads accordingly…




Now that we’ve removed our old pickup connections, it’s much easier to see what else is going on with our pickup selector switch.  The only other thing going on in my guitar (and again this may vary in your guitar so always pay close attention to your connections) is this grey 2-conductor wire which is connecting the middle lug on the pickup selector switch, to the middle potentiometer (Image 5A).  





At this point, our old pickups have been freed from their connections and it’s time to remove them from the guitar altogether.  To do this, we need to loosen the screws of our pickup mounting apparatus, and then loosen the pickup height adjustment screws.  The height adjustment screws may have a spring accompanying them -- make sure you hold on to these for later…




Now we are ready to start implementing our new pickups.  Before we cut or strip any wires, let’s get our large, insulated wires routed through their respective holes.  It may take some tinkering with (especially with the neck pickup), but all we really have to do is feed the insulated wires down through the hole in each pickup route (Image 6A).  





Once we are through, we can fasten the pickup to the mounting ring via the pickup height adjustment screws.  One easy method is to insert the height adjustment screws into the pickup mounting ring, put the springs over the screws, and then thread the screws through the mounting holes in the pickup itself.  No need to screw them all the way down, just enough to secure the ring to the pickup. Then we can fasten the pickup mounting ring down to the guitar itself…




We are all fastened down and ready to start wiring these new pickups to the switch, but first we need to strip back the black insulation to expose the internal leads.  As per our usual, just run the wire out to the necessary length, trim it, and then use your wire strippers to strip back the insulation. You should end up with something like Image 7A below…





Now we need to prep these color-coded internal leads for wiring.  This would be a good time to take a look at the reference pictures you took earlier, as well as any notes you made regarding the wiring scheme.  For me, I’ll need to make note that my green wires are ground wires. Both green wires should be stripped back, and twisted together with the both bare wires.  I’m going to pre-tin my wires as well, to make the soldering process more smooth. Once the green and bare wires are fully prep’d they should look similar to Image 8A below…





Let’s move on to the red and white wires.  For this application, these leads simply need to be stripped back, twisted together, lightly soldered as such, and then wrapped in a non-conductive insulating material (electrical tape will work perfectly).  Be careful to only twist and solder the red and white wires from each respective pickup together; do not twist and solder the red and white wires from the neck together with the red and white wires from the bridge.  Once you’ve completed these steps you should look similar to Image 9A below…





And our final prep step is that of the black (hot) wires.  These will be soldered to their respective lugs on the pickup selector switch, so let’s only strip back enough of the insulation to get the wires through the lugs and solder them in -- we don’t want to have too much extra exposed wire and risk it making contact with another conductor somewhere down the line.  Once the hot wires have been stripped back ever-so-slightly, we can pre-tin each of them. I am also going to use a solder sucker to remove the old solder from the lugs on the switch.
Once you’re fully prep’d it’s time to start soldering everything in.  In my experience, it will be easiest to start with the green and bare wires since their solder point is closer to the floor of the control cavity.  Go ahead and heat up the remaining solder on the metal jacket of the switch and get those wires in…




Then all that’s left to do is to solder the hot wires to the lugs on the switch.  Black lead from the bridge pickup goes to the bridge lug on your selector switch -- same goes for the neck side…




Before we restring our guitars and get to rockin’, it would be a safe bet to go ahead and use our multimeters to test for DC resistance.  To do this, we will need to turn our multimeters to their DC resistance setting; then place one probe on the ground solder point where we soldered in our green wires.  Next, we will need to check for resistance on each pickup by successively placing our other probe on each of the lugs where we soldered our black wires. Let’s start with the neck pickup and then move to the bridge…


Note : The correct resistance will vary depending on which pickups you are installing.  In my case, I’ll be checking for numbers roughly between 7 and 9 in accordance with Mojotone’s advertised specs for the Classic Humbuckers.  


Everything is looking good so far over here; if the same goes for you, it is officially time to fasten down the control panel cover, restring your guitar, and plug into an amp.  If you are getting bad readings, you’ll need to go back through and double-check not only the way your circuit is wired, but also the integrity of the solder joints themselves.
Check out the sound clips below to see how this affected the sound of my guitar.  The first clip is ‘before’ and the second clip is ‘after’ the pickup swap. Both clips used my Mojotone 5E3 kit amp with the same settings and same mic placement...







Well kids, that's it for today!  As always, thanks for joining in and if you have any projects you'd like to see us run through, please send your suggestions to logan@mojotone.com.  See you next time!