Question: I’m hooking up a new stereo in my car and am confused about some of the wirings. What is the ACC wire for my car stereo?
Answer: When starting your car, the radio may come on before you start the engine. This is because your stereo is connected to the ACC wire.
An ACC (Accessory) wire is a power supply line in vehicles that provides electricity to accessory devices like the radio and navigation system when the ignition is in the “ACC” or “ON” position. It allows these devices to function without starting the engine.
Ignitions typically have four stages: OFF, ACC, ON, START:
- OFF: Keeps most non-essential components turned off and inoperable.
- ACC: Powers components that are not essential for running the engine, such as stereos.
- ON: Activates fuel pumps and other necessary components to run the engine.
- START: Cranks your engine so it can start.
How to power the radio
You can power the radio in two ways. If you connect it directly to the battery, the stereo can run continuously, even when your key is in the OFF/LOCK position. A few things that are connected this way, such as the horn, brake lights, dome lights and sometimes a 12V power outlet.
However, you’ll typically only want accessories like your stereo to operate when you are driving. That’s where the ACC wire comes into play–it ensures these devices only operate when your key is in the ACC or ON position.
This setup, facilitated by the ACC wire, prevents your car battery from draining unnecessarily and ensures that the stereo and other accessories only use power when needed. The ACC wire is crucial for managing the electrical load of the vehicle efficiently and ensuring essential functions are available without compromising battery life.
Finding the ACC wire in a car stereo
Stereos generally have wires organized around a wiring harness, eliminating the need for direct power connections. To elaborate on the wiring system, generally, stereos have two positive wires:
- ACC wire: Usually red, this wire connects to a switched power source, meaning the stereo is only on when the key is in the ACC or ON position.
- Constant power source: Typically yellow, this wire connects directly to the battery to maintain settings like radio station presets, audio settings and time. Stereos that lose power even momentarily lose all their settings, which is why when you change the car’s battery, you will need to reconfigure your settings.
The bottom line
In summary, the ACC wire in your car stereo is essential for ensuring the stereo operates only when the ignition is in the “ACC” or “ON” position. This prevents unnecessary battery drain and maintains efficient electrical load management, allowing you to enjoy your stereo without compromising your vehicle’s battery life.
Xuyun Zeng is a content strategist with a wide-ranging content background including tech, journalism, cars and health care. After graduating with highest honors in journalism, Xuyun led a newspaper to win eight awards, helped start an award-winning film industry podcast and has written over a hundred articles about cars repair, state laws and insurance. Prior to joining Jerry, Xuyun worked as a freelance SEO consultant with a mission to create the best content that will help readers and grow organic traffic.
Giselle Gomez is an editor with over a decade of experience editing content across personal finance, education, travel, and sports. In editing for Jerry, Giselle’s focus is on making sure content is consumer and SEO-friendly and helping readers understand all things car ownership. In prior roles, she worked as a content strategist, syndication editor, and writer. Her work is featured in AP, NerdWallet.com, BestColleges.com, and more. Giselle holds a master’s degree from Arizona State University.
