When initially released, the El Toro came in 2 version: without preamp (passive) or with preamp (active), indicated by the ‘-E’ in the model designation. The latter turned out to be much more popular and is how almost all El Toro basses still in existence are found, including this 1983 El Toro-E. A 250kΩ Audio Taper volume potentiometer with a 200pF ceramic treble bleed capacitor, PTB circuit, i.e. a 500kΩ Audio Taper treble cut pot in series with a 47,000pF (.047µF) cap to ground and a 1MΩ Reverse Audio Taper bass cut pot with a 2,200pF (.022µF) treble bleed cap and in series with another 2,200pF (.022µF) cap to ground, and a (large black tip) 3-position pickup selector (ALCO MTA206PA) are present on both passive and active models as well as the red tip 2-way mini-toggle (ALCO MTA206N) known as the Series/Parallel “bass boost” switch. When the latter points towards the bridge, the 2 HB-2 Bi-Pole™ Magnetic Field Design humbuckers are wired in parallel which of course is only effective when the pickup selector is in the center position. With the switch towards the nut, the pups are in series and always both on; the pickup selector has no effect. The latter setting provides the bass boost by engaging a 100,000pF (.1µF) cap from the Series/Parallel switch to ground. Notice that the value for the treble cut on the passive El Toro shown below is only 250kΩ. The El Toro-E also has a white tip 2-way mini-toggle (ALCO MTA206D) with a 100kΩ±5% resistor to ground for the battery powered LM4250CN preamp: towards the bridge the bass is in high-impedance passive mode with amp/battery bypassed, towards the nut the amp is engaged and the bass is in low-impedance active mode able to drive long cables without loss of fidelity. Note that the L-2000E has a 3-position switch offering another active mode providing treble boost. The Basses by Leo website has 3 diagrams related to the El Toro-E, including this comprehensive sketch. Although its looks are much wilder, the Interceptor Bass has exactly the same (active) wiring under the covers with identical components as on this Interceptor Bass w/ash body and Interceptor Bass w/Kahler vibrato, both from 1984, and this 1985 Interceptor Bass w/maple body, all with a control panel, as well as the later ones with rear-loaded controls (see this 1987 example). Also an Interceptor Bass wiring schematic is available on the aforementioned Basses by Leo site.