ACC contact in a car: purpose, location and diagnosis

What is an ACC contact and why is it needed in a car?

If you have ever looked at the wiring diagram for a radio or other electrical equipment in a car, you have probably come across the abbreviation ACC (or Accessory). This contact plays a key role in the operation of additional devices, but many car owners do not fully understand its purpose. Let's figure out what's hidden behind this mysterious inscription and why you can't do without it when installing a multimedia system, DVR, or even a charger.

Translated from English Accessory means "accessory" or "optional equipment". Contact ACC - this is a separate electrical circuit in the ignition system that supplies power to the devices only when the key is turned to the first position (usually designated as ACC or I on the ignition switch). Unlike the constant plus (B+ or 30), which always works, and the main ignition (IG or 15), activated when the engine starts, ACC Provides power to auxiliary devices only. This allows, for example, to listen to music without turning on the ignition or use climate control in a parking lot without draining the battery.

The main advantage of this scheme is ACC contact automatically cuts off power to accessories when the key is removed from the ignition, preventing battery drain. Without it, the radio or recorder would continue to work even after leaving the car, which could lead to unpleasant consequences. However, this system also has a downside: if the contact is damaged or incorrectly connected, the equipment may either not turn on, or, conversely, remain active constantly.

Where is the ACC contact in the ignition switch?

Contact location ACC depends on the car model and the type of ignition switch, but in most cases it can be found in the back of the mechanism where the wires are connected. To get to it, you usually need to remove the plastic trim of the steering column and disconnect the connector from the lock. In the classic connection diagram, the contact ACC matches one of the following wire colors:

• 🔴 Red - the most common option (especially in Japanese and Korean cars).
• 🟡 Yellow with black stripe - often found in European cars (for example, Volkswagen or Renault).
• 🟠 Orange - typical for some American models (Ford, Chevrolet).
• 🔵 Blue - less common, but can be used in old domestic cars (for example, VAZ 2110).

To accurately identify a wire ACC, it is better to use the electrical circuit of a specific car model or a multimeter. For example, in Toyota Corolla 2010 contact ACC usually connected to the 5th pin of the ignition switch connector (red wire), and in BMW E60 - to the 15th contact (yellow-black).

How to check the functionality of the ACC contact

If the radio or other equipment does not turn on when you turn the key to the ACC, the first step is to check the contact itself. To do this, you will need a multimeter or a 12 V test lamp. The diagnostic algorithm is as follows:

1. Turn off the ignition and remove the steering column trim to gain access to the lock connector.
2. Find the ACC wire (use the diagram or use the colors from the previous section as a guide).
3. Connect the multimeter probes to the wire ACC and weight (for example, to a car body).
4. Turn the key to ACC position (first position, before starting the ignition). Voltage should appear on the multimeter screen 12–14 V.

If there is no voltage, the problem may lie in:

• 🔌 Broken wire between the ignition switch and the fuse box.
• 🔧 Ignition switch malfunctions (wear of the contact group).
• 🛠️ Blown fuse (usually F10 or F15 in the block, but check the diagram).
• 📉 Poor contact in the connector (oxidation or corrosion).

If there is voltage, but the device does not work, check the circuit further - for example, a relay in the fuse box or the connected equipment itself. In some cases, the problem lies in incorrect pinout when installing the radio. For example, if you mix up the wires ACC and IG (ignition), the device will turn on only when the engine starts.

What to do if there is no voltage at ACC?

If the multimeter reads 0V, check the fuse first (usually 10-15A). If it is intact, inspect the contact group of the ignition switch - often the contacts burn or oxidize. In extreme cases, you may need to replace the lock or bypass the relay to simulate the ACC signal.

Differences between ACC and other contacts in the ignition switch

To avoid confusion when connecting equipment, it is important to understand the difference between the main contacts in the ignition switch. There are usually four of them:

Contact	Designation	Voltage	When active	Purpose
B+ (30)	Constant plus	12–14 V	Always	Power supply for radio and alarm memory
ACC	Additional equipment	12–14 V	Key in ACC position	Operation of the radio, recorder, heated seats
IG (15)	Ignition	12–14 V	Key in ON position or when starting	Power supply to ECU, dashboard, fans
ST (50)	Starter	12–14 V	Only when starting the engine	Starter activation

Main difference ACC from IG (ignition) is that the first works only in the first position of the key, and the second - in the second (when all the instruments light up, but the engine has not yet started). For example, if you connect the radio to IG, it will turn off every time you stop the engine, which is not always convenient. On the other hand, connecting to B+ (constant plus) can drain the battery if you forget to turn off the device.

⚠️ Attention: In some vehicles (eg Nissan Almera N16) contact ACC may not be physically present, but its role is played by a relay in the fuse box. In this case, to connect the equipment you will need to use bypass circuits or program the control unit.

Common ACC contact problems and their solutions

Problems associated with ACC, usually appear as follows:

• 🎵 The radio does not turn on when the key is turned to ACC, but works from a constant plus.
• 🔋 Devices remain turned on after removing the key (battery discharge).
• 🔌 Periodic shutdown of equipment while driving.

Let's look at the most common causes and ways to eliminate them:

1. ACC wire is oxidized or broken.
   Solution: Clean the contacts or replace the wire. To check, use a multimeter in dial mode.
2. Ignition switch malfunction.
   Solution: Disassemble the lock and inspect the contact group. If there is significant wear, replace it or the entire lock.
3. Blown fuse.
   Solution: Find the fuse according to the diagram (usually 10–15 A) and replace it. If it burns out again, look for a short circuit.
4. Incorrect connection of the radio.
   Solution: Check the connector pinout ISO or Euro. In some cases the wires ACC and IG swapped places.

If the problem lies in lack of contact ACC as such (for example, in machines with a button Start/Stop), you can use a workaround - connect the equipment through a relay, which will be activated when the ignition is turned on. The diagram of such a connection looks like this:

+12V (B+) → Relay contact 85
Relay pin 86 → Ignition key (IG)
Relay pin 87 → Equipment power supply (instead of ACC)
Relay pin 30 → +12V (B+)

How to connect equipment to ACC: step-by-step instructions

Let's say you need to connect a new radio, and there is a wire in its connector ACC (usually red). Here's how to do it right:

1. Disconnect the battery.
   This will prevent short circuits when working with wires.
2. Remove the steering column trim.
   In most cars it is secured with latches or bolts.
3. Locate the ignition switch connector.
   It is usually located at the back of the mechanism and has 4–8 contacts.
4. Identify the ACC wire.
   Use a circuit or multimeter (as described above).
5. Connect the radio wire to ACC.
   For reliability, use soldering or crimp terminals rather than twisting.
6. Check your work.
   Turn the ignition to position ACC and make sure that the radio starts.

If you are installing equipment that requires constant power (such as settings memory), connect it to B+ (yellow radio wire), but don’t forget about the fuse! A typical mistake is connecting both wires (ACC and B+) to one source, which leads to malfunctions.

⚠️ Attention: When connecting powerful devices (such as a subwoofer) via ACC Make sure the wiring can withstand the load. Otherwise, the wire may overheat, leading to a fire. In such cases, it is better to draw a separate line from the battery through the fuse.

ACC in modern cars: features and nuances

In the last decade, many manufacturers have begun to abandon classical contact ACC in favor of electronic control systems. For example, in cars with a button Start/Stop (such as Toyota Camry 2018+ or BMW 5 Series G30) there is no traditional ignition switch at all. Instead, power supply to additional equipment is controlled by the unit BCM (Body Control Module), which activates the circuits only when the button is pressed without pressing the brake pedal (mode Accessory).

In such machines, connecting the equipment to ACC requires one of the following solutions:

• 🔌 Using standard connectors.
  Some manufacturers leave the conclusion ACC in the fuse box (for example, in Hyundai Solaris this is a connector C10, contact 12).
• 📶 BCM programming.
  Via a diagnostic scanner (for example, Launch X431) you can activate the mode ACC when you press a button.
• 🔄 Installing a bypass relay.
  The relay is triggered by a signal from the button Start/Stop or brake pedal position sensor.

In vehicles with the system Keyless Go (for example, Mercedes-Benz or Audi) mode ACC can be activated automatically when a door is opened or a button on the key is pressed. This complicates the connection of additional equipment, as it requires integration into the CAN bus. In such cases, it is better to contact an auto electrician to avoid mistakes that can lead to malfunctions of the electronics.

Frequently asked questions about ACC contact

Is it possible to connect the radio directly to the permanent plus (B+) so that it always works?

Technically yes, but this risks draining the battery if you forget to turn off the device. Better to use ACC or install a separate backlit switch that will remind you that the radio is on.

Why did the ACC contact stop working after replacing the ignition switch?

Most likely, the pinout in the new lock does not match or the contact group is damaged. Check the wires with a multimeter and, if necessary, re-solder them according to the diagram.

Which fuse controls ACC in my car?

It depends on the model. For example, in Toyota Corolla E150 this is a fuse IGNA (10 A) in the block under the hood, and in VW Passat B6 — S16 (5 A) in the cabin unit. Check with the electrical diagram.

Can I use the ACC pin to connect the DVR?

Yes, but keep in mind that the recorder will turn off when the key is removed. If you need continuous recording mode (for example, in a parking lot), connect it to B+ through a voltage separator or a special relay.

What should I do if my car doesn't have an ACC wire?

In this case you can:

1. Connect to IG (ignition) via a delayed relay.
2. Use button signal Start/Stop (if there is one).
3. Install an additional switch in the cabin.