• Testing pickups (impedance and functionality).
• Mapping out a switch.
• Testing a guitar cable.
• Identifying the lugs on a TRS output jack.
• Checking battery life.
Testing pickups. On many occasions I’ve used a multimeter before buying a used pickup. I learned the importance of this the hard way when I bought a used pickup at a guitar show, only to discover it didn’t work when I got it home. If I’d brought a multimeter with me, I could have tested the pickup on the spot and saved some money.
It’s a simple process to test a pickup. Set the multimeter to the ohm setting and touch its red test lead to the pickup’s primary lead (hot) and touch the black test lead to the pickup’s ground wire.
Photo 2
If you’re testing a humbucker with four conductors, make sure that the wires are properly attached to each other. For example, before you try to measure the impedance on a Seymour Duncan humbucker (Photo 2), make sure that the red and white leads are connected to each other and isolated from any other connection, and the green and bare leads are also connected to each other. Touch the red test lead from the multimeter to the black wire—the pickup’s primary lead. Touch the multimeter’s black test lead to the green and bare ground wires on the pickup. This should give you an accurate impedance measurement.
To make sense of a particular model pickup’s reading, check with the manufacturer for its exact impedance. If the impedance measurement you take is significantly lower than the manufacturer’s rating, then you know there’s something wrong with the pickup.
only to find you have no signal?
A multimeter can tell you a lot about a pickup before you wire it up. For example, humbuckers typically measure at around 8k ohms for a vintage-style pickup to as much as 25k for a high-output pickup. The 16.25k reading we see in Photo 2 indicates this is a hot humbucker. Single-coil pickups can range from 6k (vintage) up to 16k (high-output).
Mapping out a switch. If you don’t have a diagram to follow, wiring a new switch can be frustrating. An easy way to save time when tackling a wiring project is to use your multimeter to map out the switch. Simply set your multimeter to the continuity setting, which is marked with a speaker or soundwave icon. This setting will produce an audible tone to let you know when a circuit is closed.
Photo 3
On a 3-way toggle switch, for example, touch either one of the side lugs with one of the test leads from the multimeter, then touch the middle lug—that’s typically the output—with the other test lead (Photo 3). If you hear a tone, then you know the switch is on in that position. If there’s no tone in that position, the switch is off.
Photo 4
It’s a similar process for a Strat-style 5-way blade switch (Photo 4). Touch the last lug on the switch—this will be the output lug—with one of the test leads from the multimeter. Then touch each of the other lugs with the other test lead and listen for the tone. By carefully working through each switch position, you’ll be able to locate its corresponding input lug. As you map a switch’s connections, draw a diagram so you’ll have something to refer to in the future.
Testing a guitar cable. Have you ever arrived at a gig or rehearsal only to find you have no signal? The worst part is not knowing where the problem lies. Is the amp blown? Does the guitar have a loose output jack? Chances are it’s the guitar cable—that’s the place to start troubleshooting. The good news is, it’s quick and easy to test your cable with a multimeter.
Photo 5
Set your multimeter to test continuity, then touch the tip of both cable plugs with the test leads (Photo 5). If you hear a solid tone, you have a connection. But don’t stop there: Move the cable around a little to see if it has a short, and test it again. If after shaking the cable and testing it several more times you continue to get a solid tone, you can assume the cable is good. However, if the test tone is intermittent you’ll know there’s a problem. You should also test the ground on the cable. Simply touch the shaft of both plugs with the test leads and listen for a solid tone.
Testing a TRS jack. The output jacks on passive guitars are pretty simple—they have one lug for the primary lead and one for the ground. However, output jacks for an active system have three lugs. Called a tip/ring/sleeve (TRS) jack, these are common in electric guitars with active pickups or onboard circuitry, and are found in most acoustic guitars equipped with an internal preamp. The tip is for the primary lead, the sleeve is for a battery switch that turns the battery on when a cable is plugged into it, and there’s also a ground to complete the circuit for the electronics.
Sometimes the lugs for the tip and sleeve are different lengths, which makes them easier to identify, but many TRS jacks have the same length lugs with no markings to let you know which one is for the battery and which one is for the primary lead. This can be problematic if you’re installing a new pickup system into an acoustic guitar, adding active electronics to a solidbody, or troubleshooting an existing setup. But once again, the multimeter makes it easy to sort this out.
Photo 6
First plug a guitar cable into the output jack and switch your multimeter to the continuity setting. Touch one of the test leads to the tip of the guitar cable’s exposed plug and touch the other test lead to one of the lugs on the TRS output jack (Photo 6). Listen for a tone to identify which lug makes the connection. The lug that gives you a tone while you’re touching the plug tip is where you’ll attach the primary lead from a pickup or preamp.
Next, while still touching the plug’s tip with the test lead, touch the other lug on the jack. There should be no tone. Keep your test lead on that lug and move the other test lead from the plug’s tip to its shaft. You should hear a tone. This identifies the lug you’re currently touching as the battery switch for the active electronics in your guitar.
Testing batteries. Given the amount of battery-operated gear most guitarists have in their rig, it can be a challenge to stay on top of available battery power. You don’t want to arrive at a gig with a dying battery in a stomp, but you certainly don’t want to swap out all the batteries in your gear before every show. Some may still have plenty of life in them, so why not do a battery check to get the facts? (Of course, once you reach a certain number of pedals, it makes economic and ecological sense to get a powered pedalboard and be done with batteries.)
In the early days of rock ’n’ roll, guitarists would test a 9-volt battery by touching its terminals to their tongues—not a very accurate (or sanitary) approach. If you received a mild shock, the battery was deemed gig-worthy. The best way to test a battery is with a multimeter. With it, you can test just about any type of battery: AA, 9-volt, lithium, or even a disc battery.
Photo 7
Set the multimeter to the DC V setting (and if your multimeter offers it, to the appropriate voltage range). Now touch the red test lead to the plus battery terminal and the black test lead to the minus terminal. The multimeter will display the battery’s voltage (Photo 7). If you’re testing a 9-volt battery and the display on the multimeter reads less than 9 volts, the battery is weak. If the battery measures 9 volts or more, you’re good to go.
Each guitar has its own resonant frequency. Some guitars are bright, some are darker, and some are just flat-out midrange heavy. In large part this has to do with the density of the wood and the quality of the hardware, which helps explain why certain makes and models of pickups can sound fabulous in one guitar, but not so good in another. If your humbuckers sound too dark, rewiring them could be the perfect solution. It’s certainly worth trying before you replace them.
Some background. The two coils in a humbucker are typically wired in series. This produces the highest output, but also the darkest tone. If a humbucker has a 4-conductor harness, its coils can easily be wired in parallel. In this configuration, you lose about 20 percent of your volume, but the tone is brighter and cleaner.
When a humbucker’s coils are connected in series, the signal path of the first coil flows through the second coil and then on to the pickup selector switch, volume pot, and output jack. When wired in parallel, the two coils still operate together, but the signal path doesn’t travel from one coil into the other.
Photo 2
Planning the procedure. Stock Seymour Duncan JB and Jazz humbuckers are wired in series. Before we can modify the 4-conductor harness to wire the coils in parallel, we need to understand the Duncan color codes (Photo 2). Except for the bare ground wire, each colored wire is either the “start” or “finish” of a coil. How these wires are connected determines whether the pickup is wired in series or parallel. Here’s the breakdown:
• Black is the start of coil 1.
• White is the finish of coil 1.
• Green is the start of coil 2.
• Red is the finish of coil 2.
• Bare wire is always the ground.
Note: This applies only to Duncan pickups—other manufacturers use different color-coding schemes. See “Obey Your Color Codes” for more details.
Photo 3
Photo 3 shows these five wires connected in a series configuration. We have the black wire acting as the hot or primary lead, and the red and white wires are soldered together to create the series link (that is, they connect the two coils).
Fig 1
The green wire is connected to the bare wire and then soldered to the back of a pot to create a ground. Figure 1 shows how the hot wires connect to the 3-way blade switch for series wiring, and how the switch itself is configured.
Photo 4
Photo 4 illustrates how to connect the wires of a 4-conductor Duncan humbucker in a parallel configuration. As you can see, black and red are joined—they become the hot or primary lead. White and green are connected to the bare wire to become the ground, and all three are soldered to the back of a pot. The parallel wiring diagram for the 3-way switch is show in Figure 2.
Fig 2
By wiring the humbucker in parallel, we have connected the start of coil 1 to the finish of coil 2. For the ground, we have connected the finish of coil 1 to the start of coil 2 and both are joined to the bare wire.
Doing the deed. After removing the strings and pickguard, unsolder the pickup wires from the switch and pots, being careful not to overheat them. Separate the wires from each other with your soldering iron. Next, twist and solder the black and red wires together. Do the same for the green and white wires, and join them to the bare wire. Now solder the black and red to the input lug on the 3-way switch, and the green, white, and bare wires to the back of one of the pots.
That should do it. Put the pickguard back on, restring, and test out your new tones.
Obey Your Color Codes
Different pickup manufacturers use different color codes for their 4-conductor humbuckers, so before you start brandishing that hot soldering iron, make sure you’ve got the right color codes and have figured out how to connect the wires. Here are a few parallel wiring combinations for several other popular pickup manufacturers.- DiMarzio: Red and white are hot, black and green are ground.
- Gibson: Black and white are hot, green and red are ground.
- Jackson: Green and red are hot, white and black are ground.