Wiring an 8-gang switch panel: what goes where

Two boxes, one loom.

The control box bolts up in the engine bay. The panel sits on the dash. The only thing crossing the firewall between them is a signal cable, and that is the whole point of the design: the current that runs your lights never enters the cabin. Every decision below follows from that.

Work out the current before you pick up a tool

Open the spec sheet for the panel you have and find the per-channel line. On a TC-SW8 it reads:

Add those up and you get 130A. The panel is rated at 60A. That is not a contradiction and it is not a printing error — it is the number that catches people out.

The per-channel figure is the most any one circuit may draw. The 60A is the most the panel will pass with everything running at once. You size each circuit against the first number and your worst-case simultaneous load against the second. A TC-SW12 works the same way: twelve circuits rated 2×30A, 4×20A, 3×10A and 3×5A — 185A on paper, 100A in practice.

Work in watts if that is easier. The TC-SW8 is rated 720–1440W, which is the same 60A expressed at 12V and at 24V. Higher system voltage, same current ceiling, twice the power.

A worked example. A TC-Q90C driving light is a 90W lamp. At 12V that is 7.5A, so it belongs on a 10A channel — the 5A channel is not enough and the 30A channel is wasted on it. Run a pair off one circuit and you are at 15A, which means the 20A channel. At 24V the same pair draws half that.

Do the sum for the circuits you will switch on together, on the worst night you can imagine: light bar, driving lights, work lights, fridge, compressor. That total is the number the panel has to survive, and it is the one people estimate instead of adding up.

Where the control box goes

In the engine bay, against the firewall, on the side away from the exhaust and the turbo.

The TC-SW8 is rated IP65 as a unit. That is sealed against dust and against water from a hose, and it is not the same as being safe underwater or under a pressure washer held a hand’s width away. Mount it where road spray reaches it, not where a wheel throws standing water at it.

Watch the temperature too. The rated range is -40°C to 105°C, and that is the electronics inside the box, not permission to strap it to a manifold. Ambient under a bonnet on a slow climb in summer gets closer to that number than most people expect. Give it air.

Worth knowing: not every panel in the range carries one rating for the whole product. The TC-SWT10 is quoted as control box IP67 / screen IP65 — two enclosures, two ratings, stated separately for a reason. The box that lives in the weather is sealed harder than the screen that lives on your dash. If you are fitting a TC-SWT10, that is the number that applies to the part under the bonnet.

Where the panel goes

Somewhere you can reach without taking your hand far off the wheel, and see without taking your eyes far off the track.

Decide the layout before the adhesive goes anywhere near the dash. A TC-SW8 ships with 70 OEM icon options so the panel reads like a factory fitment rather than an aftermarket add-on — pick the icons, lay them out, live with the arrangement for a day, then commit. Peeling a decal back off a textured dash panel is not a five minute job.

Check which control you are actually fitting while you are at it:

• TC-SW8B takes the Bluetooth module as an option, not as standard. Check which way yours was built before you count on the app.
• TC-SW8W ships as two panels — the wired main panel for the dash, plus a wireless remote good for about 30m from the vehicle on 433MHz. The remote is a radio handset. The app talks Bluetooth to the wired panel, not to the remote.
• TC-SWT10 replaces the button panel with a 5-inch 1920×1080 screen that dims itself off an ambient light sensor.

Fit the one you have. The mounting work is the same; what differs is how many ways there are to turn a circuit on.

Crossing the firewall

Use a hole that already exists. Every vehicle has a rubber grommet where the factory loom passes through, and going through it beats drilling every time — a drilled hole is a rust site and a chafe point, and it is the repair you will be doing in three years.

The principles, in order:

1. Existing grommet first. Slit it, pass the cable, seal it again.
2. If you must drill, fit a grommet. Bare metal edge against insulation is a short waiting for a corrugation to shake it loose.
3. Leave a drip loop. The cable should approach the firewall from below the entry point so water runs off the low point instead of tracking along the sheath into the cabin.
4. Cable-tie to the factory loom. A cable strapped to something that is already secured cannot flap, chafe or get caught. Never let it cross open air between two anchor points.

Most vehicles have more than one candidate. Look behind the dash on the driver’s side, where the main loom comes through, and under the scuttle where the wiper and washer lines run. Take the one with slack in it — a grommet you have to stretch to reach is a grommet that will not reseal.

Once the cable is through, check three things before you move on. The grommet closes around it again, with sealant if you slit it. The cable is clear of the pedal box and the bonnet hinge through their full travel. And it does not pull tight when the engine rocks on its mounts — an engine moves further under load than it looks like it should, and a cable stretched across that gap is a cable that will chafe through in a season.

Power and earth

The supply comes off the battery to the control box, with protection at the battery end — a fuse at the source protects the cable, and the cable is what burns if it chafes. Protection at the far end protects nothing along the run.

Earth matters as much as the positive and gets a fraction of the attention. The TC-SW12 is specified for isolated positive and common ground wiring: every circuit returns to one earth point, and that point wants clean bare metal, a star washer and a bolt that is actually tight — not a painted bracket, not a seat rail, not whatever was nearest.

We do not publish a cable size or a fuse rating for your build, because we have not confirmed one. Size the cable to the channel rating and to the length of the run, not to the lamp’s sticker, and have it checked by someone qualified if you are not certain. A number invented to fill a gap in a guide is the number someone wires their vehicle to.

What the panel does and does not do is worth being precise about here. The TC-SW8 uses solid-state electronic switching — no relay contacts to weld shut or chatter, and channels rated individually. The TC-SWT10 goes further, with electronic-fuse switching on every channel plus a per-channel working monitor with overcurrent protection, and LVCO low-voltage cut-off that protects the starting battery when you are parked up. Neither replaces protection at the battery.

Before you connect the battery

1. Every crimp pulls against hand force without moving.
2. No conductor is visible outside a terminal or a heatshrink.
3. The signal cable is tied down along its whole run, with a drip loop at the firewall.
4. The earth bolt is on bare metal and tight.
5. Nothing touches the exhaust, the steering shaft, or anything that moves through its full travel — check the lock-to-lock, not the straight-ahead.

Then connect, and test one circuit at a time before you put the trim back.

The mistakes worth naming

Earthing to whatever was nearest. A painted bracket, a seat rail, a bolt into a plastic-backed panel. It will work on the driveway and fail in the wet, and the symptom is never obviously an earth — it is lights that dim when the compressor runs, or a circuit that drops out over corrugations. Bare metal, star washer, tight bolt, one point for the panel.

Protecting the wrong end of the cable. A fuse at the panel end leaves the whole run from the battery unprotected, and that run is the part that lies against sheet metal. The fuse goes at the source, close to the battery terminal.

Sizing the circuit to the lamp instead of the channel. The rating on a channel is the ceiling, not a recommendation, and the wattage on a lamp is a steady-state number. Pick the channel that covers the load with headroom — the TC-Q90C example above sits at 7.5A on a 10A channel, not at 7.5A on the 5A one because the arithmetic nearly works.

Committing the icons too early. Cosmetic, but it is the one that costs an afternoon. Lay the 70 icon options out, sit in the driver’s seat, and only then peel a backing off.

Where to go from here

Eight circuits covers most builds: lights front and rear, a compressor, a fridge, a couple of spares for whatever you add next season. If your list is already longer than eight, size up now rather than fitting a second panel later — the TC-SW12 gives you twelve circuits and 100A instead of 60A, and the wiring work is the same work.

If you want to see how the pieces sit in the vehicle before you commit to a mounting position, the diagram on the TC-SW8 product page shows the control box, the dash panel and the cable between them in a side view.

Fitting the wireless kit instead? Everything above still applies, and there is one extra part to place — where the control box and the antenna go on a TC-SW8W covers it, with the dimensions of all four pieces.

And if you are not sure your load fits inside 60A, send us the list of circuits and what each one draws. We will tell you which panel covers it — or that none of ours does.

Where it goes

Two boxes, one loom

The control box carries the current and lives in the engine bay. The panel only carries signal, so the cable through the firewall is thin and easy to route.

1. 1

   Control box — engine bay

   Carries every amp. Mounts on the inner guard or firewall, fused channels facing down, battery leads straight to the terminals.

2. 2

   Wired main panel — within reach of the wheel

   Signal only, so one thin cable through an existing firewall grommet. Mounts on the dash, a pillar or an overhead console.

3. 4

   Phone app — the same eight channels

   Everything the panels switch, plus the setup the buttons cannot do:

   • Backlight colour, per switch
   • Icon, per switch — the same 70-icon set
   • Mode, per circuit — toggle, momentary, flashing or strobe
   • Grouping, so one tap drives several circuits

   Over Bluetooth — and the radio sits in the wired main panel, not in the remote, so the app works close to the vehicle. When you need distance, the remote is the tool. On this model the Bluetooth module is an option, not fitted as standard.