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Installing a car amplifier is a weekend job for most people, and the steps are the same whether it’s a 300 W mono amp for one sub or a 1,200 W amp for two. The parts that matter most aren’t the hard ones: a correctly sized and fused power wire, a solid ground and a properly set gain. Get those right and the system will be quiet, reliable and loud. Here’s the whole process, in order.
The short version
- Size the wire to the amp: about 8 AWG copper to 475 W, 4 AWG to 1,200 W, 1/0 above that on a typical 17-foot run.
- Fuse the power wire within 18 inches of the battery.
- Ground to bare chassis metal with a short wire the same gauge as the power wire.
- Signal: RCA from an aftermarket radio, or speaker-level input or a line output converter for a factory radio.
- Set the gain to match the radio’s output, not to make it as loud as possible.
What you’ll need
| Part | Notes |
|---|---|
| Amp wiring kit | Power wire, ground wire, fuse holder and fuse, remote wire, RCAs. See our wiring kit picks. |
| Speaker wire | 12 AWG copper for most single-sub installs |
| Line output converter | Only if your radio has no RCA outputs and your amp lacks speaker-level inputs |
| Tools | Wire strippers, crimper, socket set, drill, multimeter, zip ties, panel tools, grommets |
Pick the right wire gauge
| Amp RMS power | OFC copper wire | Kit example |
|---|---|---|
| Up to about 475 W | 8 AWG | Most small-amp kits |
| Up to about 1,200 W | 4 AWG | Rockford RFK4X or Skar 4 AWG |
| Up to about 1,900 W | 2 AWG | 2 AWG copper kit |
| Up to about 3,000 W | 1/0 AWG | Skar 1/0 AWG |
These figures assume 13.8 V, a Class D amp at about 80% efficiency, a 17-foot run and no more than half a volt of drop. Copper-clad aluminum (CCA) needs one to two sizes thicker depending on run length. Our wire gauge calculator works it out for your car.
Step 1: plan and disconnect
- Decide where the amp goes: under a seat, on the back of the rear seat or on a trunk wall. It needs airflow and must be screwed down.
- Plan the power route from the battery to the amp, along one side of the car, and the signal route along the other side to avoid noise.
- Disconnect the battery’s negative terminal before you do anything else.
Step 2: run the power wire
- Find a rubber grommet in the firewall, or use a dedicated pass-through. Never run power wire through bare metal without a grommet.
- Feed the wire into the cabin and route it under trim panels or carpet to the amp location.
- Mount the fuse holder within 18 inches of the battery and connect it to the positive terminal. Leave the fuse out until the end.
- Match the fuse to the wire, not the amp: it protects the wire from catching fire if it shorts.
Step 3: make a solid ground
- Find a spot on the chassis close to the amp: a seat bolt is not ideal; a bolt into bare body metal is.
- Sand off paint to bare metal, then bolt down a ring terminal on the ground wire.
- Keep the ground wire short, ideally under 18 inches, and the same gauge as the power wire.
- Protect the bare spot from rust with a little paint or grease after tightening.
Step 4: connect the signal
- Aftermarket radio: run RCA cables from its subwoofer output to the amp.
- Factory radio, amp with speaker-level inputs: tap the rear speaker wires (or the factory sub wires) and connect them to the amp’s speaker-level input. The Kicker CXA amps in our monoblock guide have this.
- Factory radio, amp without speaker-level inputs: use a line output converter such as the AudioControl LC2i or Kicker KISLOC2. Our converter guide explains which suits your car.
Step 5: connect remote turn-on
The amp needs a 12 V signal to switch on with the radio. Use the radio’s remote or amp-turn-on wire (usually blue/white), the remote output of a line output converter, or the amp’s own signal-sense or DC-offset turn-on if it has one.
Step 6: wire the sub
Run speaker wire from the amp’s outputs to the sub or box terminals, keeping polarity consistent. If your sub has two voice coils, wire them to a load your amp is rated for; our dual voice coil wiring guide has every combination. Measure the load with a multimeter before you power up.
Step 7: power up and check
- Double-check every connection, then fit the fuse near the battery and reconnect the negative terminal.
- Turn on the radio. The amp’s power light should come on, with no protect light.
- Play music quietly and check the sub plays. If it doesn’t, check the remote wire first.
Step 8: set the gain and filters
- Set bass boost to zero and the amp’s low-pass filter to around 80 Hz. If the box is ported, set the subsonic filter a few hertz below its tuning.
- Turn the radio’s volume to about three-quarters, with its EQ flat, playing a bass test tone or bass-heavy track.
- Raise the gain slowly until the sub is loud and clean, then back off a little at the first sign of distortion.
- For precision, use a multimeter: target AC voltage = √(power × impedance). For 500 W at 2 Ω, that’s about 31.6 V at the speaker terminals with a test tone.
Gain is not a volume knob; it matches the amp to the radio’s signal. Set it too high and you clip the signal, which is what usually damages subs. Our clipping guide explains why.
Safety first: disconnect the battery’s negative terminal before you start, fuse the power wire within 18 inches of the battery, and use a professional installer if you’re not comfortable working on your car’s electrics.
Common problems
| Symptom | Likely cause |
|---|---|
| Amp won’t turn on | Remote wire, blown fuse or bad ground |
| Alternator whine | Poor ground or RCA cables next to power wire |
| Amp goes into protect | Load too low, short in speaker wire, overheating |
| Headlights dim on bass | Wire too thin or charging system needs an upgrade |
| Rattles everywhere | Loose panels; see our rattle fix and deadening mats |
FAQs
Do I need a capacitor?
For most systems under about 1,000 W, no. Correct wire size and a good ground matter more.
Can I ground to the battery negative?
You can, but it means a longer ground run. A short chassis ground near the amp is standard and works well when done properly.
What is the Big 3 upgrade?
Upgrading the alternator-to-battery positive, battery-to-chassis and engine-to-chassis wires. It helps bigger systems, usually above 1,000–1,500 W.
How long does it take?
Most first-timers take an afternoon to a full day, mostly removing and refitting trim.