“When last we left our intrepid hero, he had just removed all the electronics from the ’08 Epiphone Les Paul Standard Plain Top. In today’s exciting episode, we will be captivated as he prepares the guitar to receive the transplant, and creates a new wiring harness from scratch”.
Ok, that may be a bit mellow-dramatic, but I always did love the old radio shows. Now that I’ve prepped the guitar by removing the old electronics, and I’ve prepped myself by adding a few of my favorite Blue beverages from our Canadian friends, it’s time to create the wiring harness.
One important difference between the harness that I just took out, and the one that I’m about to make is the shaft size of the pots. Epiphone stock pots have slightly smaller shafts than the CTS pots. In order for the new pots to fit, we need to enlarge the holes (Gibson uses different pots which require the larger hole, so this is not needed). Some people have suggested using a reaming tool to enlarge the holes. I feel that is overkill, since the holes only need to be worked a small fraction of an inch, and I feel the reaming tool may harm the finish (the Epiphone poly finish has a tendency to flake). I prefer working the holes with 60 and 220 grit sandpaper. Yes, it takes a bit longer, but the finished product is better.
You’ll need to open up the holes for the pots just ever so slightly. I use 60 and 220 grit sandpaper. Cut a 4×4 inch piece of both grits and roll them up. Put them in the holes and gently work the sandpaper up and down while slowly rotating the sandpaper in the hole. Start with the 60 grit, and constantly check to see if the pot fits. You don’t want to make the holes too big. When the pot just barely doesn’t fit in the hole, finish it off with the 220 grit sandpaper until the pot fits snugly, but is not tight. Also, you won’t have to worry about hurting the finish. It’s important to open the holes before you make the harness. Since we use one of the new pots to check the size of holes as we sand them, you don’t want to move the completed harness around every time you want to check the holes.
The hole directly above the tailpiece has already been finished. You’ll see it looks clean and all the finish has been removed from inside the hole compared to the others.
We need to create a template of the pot holes so we get the spacing right when we build our new harness. Take a blank piece of paper and tape it to the front of the guitar so the paper covers the holes for the pots. Flip the guitar over and from inside the electronics cavity use a pen to draw circles on the paper using the holes as a guide. Make sure you label which pots are neck and bridge, and volume and tone. Remove the paper from the guitar and tape it to a thin piece of scrap wood. This will become our template.
With the paper taped to the wood, and using a 3/8” bit, drill 4 holes through the circles on the paper into the wood. Off to the side, away from the 4 holes you just drilled, drill a ½” hole to mount the toggle switch.
At this point I should probably talk about pot values and placement. Even the best set of matched pots from Jonesy or MSSC won’t all be the same value. Because of this, the experts have figured out where each pot should go. The pot with the highest value should be the neck volume pot to give the pickup as much clarity as possible. Next should be the bridge volume, then neck tone, and finally bridge tone. To get the value of a pot, use a multi-meter set to measure resistance. Put the probes on the outer lugs. The resistance shown on the multi-meter is the value of the pot. Matched sets from several vendors will already be labeled with both value and placement, such as “NV” for Neck Volume. You’ll have to measure the pots yourself if you order the pots from StewMac or Allparts.
Now that we know which pot should go where, put the pots in the holes. The neck volume lugs should facing the neck tone lugs. The goes for the bridge pots, too. Finally, put the toggle switch in the hole. We don’t want anything moving while we have a hot soldering iron it, so put the nuts on the pots and switch and finger tighten everything down. Since we’re all guitar players here, we should have above average finger strength. 🙂
So, before we start soldering wires I’d like to state the obvious (my wife always says I have an amazing grasp of the obvious). Test every solder joint as soon as you’re done. Don’t go a few steps and then test. Test immediately. It will save you so much time in the end. Also, make sure you test all the connections. In places where you are soldering a wire to two lugs at the same time, test both lugs against each other and with the wire. I cannot stress enough how important it is at this stage to take your time and constantly test, test, test!
I’ve always found it easier to start off slowly, so I wired up the switch first. In the picture above, the two lugs coming off the left side of the switch will go to the jack. On the left side, there are two lugs which will connect to the volume pots, and one big loop which is the ground. Using a pair of pliers, bend the two lugs on the left together (opposite side from the ground), and then solder a 2’ piece of shielded wire to the lugs. Next, we take 2 more pieces of 2’shielded wire and solder them to the lugs on the opposite side (one to each). Now that we have the leads soldered to the switch, we need to ground the whole thing. Since I’m using vintage push-back wire with an exposed braided shield, I took a 6” piece of exposed solid 22 gauge wire and soldered it to the grounding lug. Then I wrapped the other end around the braided shielding of the 3 wires coming off the switch and soldered it to shielding. While we are testing the switch to make sure it works as it should, it’s a good idea to label the wires for future reference (Neck, Bridge, Jack are the labels I use).
With the switch done, and the soldering iron ready to go, I moved on to wiring up the pots with the caps and ground loop. Since we’ll be soldering to the back of the pots, now is a good time to switch the tip on the soldering iron to the blade to provide a larger surface area to heat the pots quicker. The next step is to ground the lugs on the pots. For the tone pots, bend the center lug back until it is touching the pot casing. You probably won’t get it all the way back, but get it as close as you can. Now, solder the lug to the casing. Be very careful that you don’t let any molten solder run down into the small holes in the pot casing. This can kill the pot, or at the very least cause a “bump” in the action of the pot. Do I need to tell you to test it to make sure the lug and casing have a good connection? Didn’t think so. 🙂 For the volume pots, look at the pot so the three lugs are pointing down. Bend the lug on the right backwards until it is touching the casing, just like tone pots. Again, solder the lug to the casing. Do this for both the neck and bridge volume pots.
Since I still had the blade tip on the soldering iron, next I created the ground loop between all of the pots. I used a piece of insulated, not shielded, 22 gauge wire and cut it to size so it creates an arc around all four pots starting with the neck volume pot and ending with the bridge volume pot. Strip the insulation from the wire at the ends, and in the two places in the middle where it will be soldered to the neck and bridge tone pots. It’s perfectly acceptable to use a bare wire without any insulation as the ground loop wire. Just make sure it’s tight, and can’t vibrate or move and short something out. Since I don’t have the precision of the pre-made kits, I opted for some flexibility and used the insulated wire. Once the ground wire is soldered to all the pots, use your multi-meter to make sure you have continuity from the back of each pot to the back of every other pot.
The last step is to solder the tone capacitors between the volume and tone pots. Since this is delicate soldering work, I suggesting switching back to the fine point soldering tip. Using the picture above of the pots on the template board, the tone caps go from the lower lug on the tone pots to the middle lug on volume pots. Most capacitors don’t have any “directionality”, so it doesn’t matter which end goes on the tone pot or the volume pot. When you’re done, you should have something that looks like this:
There you have it. The switch and harness are wired, and ready to be installed in the guitar. Next time we’ll finish off the electronics upgrade be installing the switch and soldering everything together.
Until next time, have another drink. The more you drink, the better I sound.