Install manual for the McGrath 12-way pickup selector (original board, firmware fw=5) in a bass. Updated October 2026.
Download the PDF manual (2 pages, includes the wiring diagram).
The board is about 29 × 40 mm and runs on 18 V from two 9 V batteries in series, or on a single 9 V battery. It draws about 18–23 mA whenever it has power.
Both GND terminals must go to ground or the switch won't turn on.
What you need
| Item | Notes |
|---|---|
| 12-way board | Four screw terminals on the top edge, six on the bottom edge, USB-C at the top left |
| Wera 05118003001 screwdriver | Use it for every screw terminal (KF128, 2.54 mm pitch). Larger blades chew the screw heads |
| One or two 9 V batteries with clips | Two in series give 18 V; one 9 V also works |
| Output jack | Tip for the signal, sleeve for ground |
| Hook-up wire, 22–26 AWG stranded | Red for battery +, black for ground, any colours for pickups |
| Wire strippers, soldering iron | The iron is for the jack and the volume pot lugs |
| Knob for the encoder shaft | Bourns PEC11R encoder; washer and nut go on from the front |
| Insulating tape or a thin foam pad | Keeps the board off cavity shielding |
| Computer, USB-C cable, McGrath Editor (optional) | To set favourites and enabled positions |
Wiring connections
The full wiring diagram is in the PDF. In short:
| From | To |
|---|---|
| Battery + (red) | BAT+ terminal. With two batteries, the first one's – links to the second one's + |
| Battery – (black) | Common ground: a GND terminal or the output jack sleeve |
| Both GND terminals | Output jack sleeve (common ground). Both are needed for the switch to turn on |
| HOT | Volume pot input lug. The pot's wiper (middle lug) goes to the jack tip, its third lug to ground |
| Bridge, Middle, Neck pickups | B+/B–, M+/M–, N+/N– (+ is the pickup's hot/start wire, – its return) |
Before you start
- Take the batteries out and unplug the cable from the jack.
- Label the old wires before you cut them. Mark each pickup's two wires (+ and –) for Neck, Middle and Bridge.
- Check the cavity. The board needs about 30 × 40 mm of floor space and room for the relays on both sides.
- Don't tin stranded wire that goes into a screw terminal; the solder creeps and the wire works loose. Twist the strands and strip 4–5 mm.
Connecting the terminals
Loosen each screw with the Wera 05118003001, push the bare wire fully in, tighten firmly and tug the wire to check it holds. Positions below are seen from the terminal side, the side that faces you inside the cavity.
| Terminal | Wire to |
|---|---|
| Top row, left to right (after the USB-C socket) | |
| GND (power) | Common ground: output jack sleeve. Battery – can go here too |
| BAT+ | Battery +. With two batteries, link the first one's – to the second one's + |
| GND (output) | Output jack sleeve |
| HOT | Volume pot input lug. The pot's wiper (middle lug) goes to the jack tip and its third lug to ground |
| Bottom row, left to right | |
| B+ and B– | Bridge pickup, hot (+) and return (–) |
| M+ and M– | Middle pickup, hot and return |
| N+ and N– | Neck pickup, hot and return |
| Battery – | Common ground: a GND terminal or the output jack sleeve |
The two GND terminals are separate on this board (power and output). Both must go to ground or the switch won't turn on. The board has no reverse-battery protection: check that BAT+ goes to battery + before you connect the batteries. If the printed labels on your board read differently from this table, follow the labels.
Fitting the board
- Push the encoder shaft out through the knob hole from inside, with the terminal side facing you. Fit the washer and nut from the front and tighten until the board can't turn.
- Put insulating tape or a foam pad over any shielding paint or foil the board could touch.
- Dress the wires clear of the relays and the cavity cover. The USB-C socket stays reachable with the cover off.
- Fit the knob and batteries, test, then close the cover.
First power-up and use
- Connect the batteries and plug a cable into the jack. The relays click to the saved position.
- Turn the knob through all 12 positions with the bass into an amp at low volume. Each click should change the sound, and position 12 wraps back to 1.
- Try the button: one click jumps between your favourite and the last position, three clicks go to position 1, and a long press stores the current position as the favourite.
Battery life is about 20–25 hours of powered time on two batteries, and roughly half that on one. The Editor's idle setting (ps) can switch the relays off after a set number of minutes, but that drops the bass to the position 1 sound until you touch the knob.
McGrath Editor. Plug USB-C into a computer and open McGrath Editor 0.1.5 to set enabled positions, favourite, long-press time, step delay and remember-position. Unplug USB before playing through an amp, or a ground loop may cause hum.
Troubleshooting
| Problem | Check |
|---|---|
| No sound in any position | HOT and output GND wires, the volume pot lugs, jack tip and sleeve |
| Knob does nothing, no relay clicks | Both GND terminals on ground, BAT+ polarity, battery charge |
| One pickup missing | That pickup's two terminal screws; tug the wires |
| Combined positions sound thin | One pickup is backwards: swap its + and – |
| Board needs re-flashing | Hold the boot button SW2 while plugging in USB, then load mcgrath-relay-v5.hex with the Editor's flasher |
Don't load the new low-power firmware onto this board. It is written for the redesigned boards, and on this one the relays won't switch.
Questions about your install? Send us a message.