Amplifier · subwoofer · power cable
Car amplifier wiring: power, ground and remote turn-on
An amplifier is the biggest load most cars ever get after the starter: a 600 W amp can pull 50 A on bass notes. It needs a thick power cable fused at the battery, an equally thick short ground, and a thin REM wire that switches it on with the radio.
Open the editor · ▶ Run the live demo
The four connections
- Power: battery + → fuse within ~30 cm of the battery → cable through the firewall (in a grommet) → amp B+.
- Ground: amp GND → bare metal near the amp, under 1 m, the same size as the power cable.
- REM: the head unit’s remote / amp turn-on output (often blue-white) → amp REM. It carries almost no current.
- Signal: RCA cables (or speaker-level input) down the other side of the car from the power cable.
Typical loads on 12 V
| Load | Power | Wire length | Current | Fuse | Wire |
|---|---|---|---|---|---|
| Parking lights | 10 W | 4 m | 0.83 A | 2 A | 0.35 mm² (22 AWG) |
| Headlight bulb H7 | 55 W | 3 m | 4.58 A | 7.5 A | 0.75 mm² (18 AWG) |
| Pair of headlights | 110 W | 3 m | 9.17 A | 15 A | 1.5 mm² (16 AWG) |
| Horn | 60 W | 2 m | 5 A | 7.5 A | 0.5 mm² (20 AWG) |
| Wiper motor | 120 W | 2 m | 10 A | 15 A | 1 mm² (17 AWG) |
| Radiator fan | 250 W | 2 m | 20.83 A | 30 A | 4 mm² (12 AWG) |
| LED light bar | 300 W | 4 m | 25 A | 35 A | 6 mm² (10 AWG) |
| Audio amplifier | 1000 W | 5 m | 83.33 A | 125 A | 35 mm² (2 AWG) |
Cable and fuse by amplifier current
| Amplifier draw | Fuse at the battery | Power and ground cable (5 m run) |
|---|---|---|
| 30 A (≈ 360 W) | 40 A | 10 mm² |
| 50 A (≈ 600 W) | 70 A | 16 mm² |
| 80 A (≈ 1000 W) | 125 A | 35 mm² |
Size by the current the amp actually draws (or its fuse rating), not by the “peak watts” on the box. The fuse protects the cable, so it is chosen for the cable.
See also: Automotive wire gauge chart · Voltage drop calculator
Check the power side in the simulator
- Run the live demo: a 70 A fuse at the battery, 16 mm² power and ground, the head unit and its REM output.
- Turn on ACC: the head unit plays, the amp stays off. Close REM: the amp switches on and draws about 50 A.
- Click the power cable: a 5 m run of 16 mm² loses under 0.3 V. Try 6 mm² to see the overload warning.
Questions
Why does my amp turn on but make no sound?
REM and power are fine, so look at the signal side: RCA cables, gain settings, protection mode from a bad ground or a shorted speaker.
Do I need a capacitor?
Rarely. Dimming lights mean voltage drop: a thicker power and ground cable, a short ground and a good battery fix it properly.
What is the “Big 3”?
Upgrading the battery–body, engine–body and alternator–battery cables, so high current reaches the amp with less drop. Worth it with large systems.
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