G&L tech resources: Wiring harnesses


Most everybody uses only treble cut controls to adjust the tone. Take Les Paul (inspired) guitars, where each pickup has a separate tone pot. It is true for Telecaster (inspired) guitars with a shared tone control for both pickups. It is even true for Stratocaster (inspired) guitars, where those from the 1950s have a separate tone control on the neck and middle pickup, as does this (4-bolt) George Fullerton Signature. The modern Stratocaster has a separate tone control on the bridge pickup while the middle and bridge pickups share a control. Leo Fender definitely changed it up by making the tone stack work like any radio or amplifier with separate treble cut and bass cut. Indeed, when inspecting his Passive Treble and Bass (PTB) circuit design, it echoes Peter Baxandall’s original “Negative-Feedback Tone Control” paper published in Wireless World in October of 1952, a design ubiquitous in hifi audio equipment, amplifiers, and even guitar effects. Using similar terminology as in that paper, the PTB circuit misses the ‘Lift’, it is passive after all, but provides separate treble ‘Cut’ and bass ‘Cut’. This allows the player to control both extremes of the sonic spectrum.

For the “Improved Strat” guitars, G&L uses pretty much the same as any other manufacturer for the volume control: a 250kΩ Audio Taper potentiometer with some treble bleed capacitor. In the wiring harness of the F-100 one finds a 20pF cap but when the S-500 was introduced in 1982, the value had been upped to 100pF. Another difference is the use of a 1MΩ Audio Taper treble cut pot, instead of 250kΩ, still in series with a 22,000pF (.022µF) cap from the wiper to ground. Its bass cut control is a 1MΩ Reverse Audio Taper pot with a 2,200pF (.0022µF) treble bleed cap across the pot. As pictured, the same harness is found on the Nighthawk, introduced in 1983. As discussed elsewhere, the S-500 and Nighthawk sound differently due to a slight change in construction, placement, and orientation of their pickups.

In mid-1984, after the Nighthawk had been renamed to the Skyhawk, Leo redesigned its circuitry by changing the treble bleed cap on the volume pot to 200pF and reducing the value of the treble cut pot to 500kΩ, differentiating it even more from the S-500. Such a harness is found on a Skyhawk w/Kahler from 1986, but was later also used on other models, including this “late first style” S-500 from 1988, the BBE-era Legacy Special from 1996, all the way to the 2017 Doheny. The shown block diagram for the Legacy Special, drawn by Paul Gagon in 1998 and obtained via the archived G&L website, lacks the 200pF cap clearly visible on the volume pot in the pictures. Likewise, the diagram for the Legacy, available on the same archived site and included below for convenience, does not show a 200pF treble bleed cap either but, even with all guitars in the collection, its correctness cannot be verified at present. Suffice it to say the Legacy (SSL-2) has such a cap on the volume pot even though the rest of its harness does not match the PTB circuit.

Around 1988, when the S-500 and Skyhawk both got a single pickguard, a 1,000pF (.001µF) cap between the wiper and ground was added to the bass cut control (see this 1988 Skyhawk). In addition, the S-500 received an expander switch, allowing the combination of neck and bridge as well as all 3 pickups together. The shown diagram is correct as demonstrated by this 1991 S-500 Signature. This option also became available for the Legacy like on this Phyllis model: ‘Blondie’ from 2008. But its harness differs from both the aforementioned S-500 with expander switch diagram, since the 1MΩ Reverse Audio Taper bass cut pot on ‘Blondie’ lacks the 1,000pF (.001µF) cap, and the Legacy diagram, since the 250kΩ Audio Taper volume control has a 200pF treble bleed cap. Which only leaves the 500kΩ Audio Taper treble cut pot with a 22,000pF (.022µF) treble bleed cap as the correctly depicted component.

Note that the PTB circuit on early L-series basses or guitars like the F-100 or Cavalier are different by using a 250kΩ pot and/or a 47,000pF (.047µF) cap for the treble cut control instead. For those instruments, see the previous sections for more details. In a 2012 tonefiends archives post on the Seymour Duncan website, Senior Contributing Editor to Premier Guitar Joe Gore advises to use three 500kΩ pots when installing the PTB circuit on a double (non-MFD) humbucker guitar.


PTB circuit - Strat style guitars