Why will my car stereo not switch on?
If your car stereo will not switch on after installation, it is often because it is not receiving the correct power supply. For example, the ignition-switched supply may be missing, the wiring may be incorrect or the car may require a specific installation adapter.
Here are some of the most common causes and how to troubleshoot the problem.
1. Check that the stereo receives both a permanent supply and an ignition-switched supply
Most aftermarket stereos need two separate power connections:
Yellow wire (BATT): Permanent 12 V from the battery. Used, among other things, to retain the stereo’s settings.
Red wire (ACC): Ignition-switched 12 V that tells the stereo when to switch on and off.
Black wire (GND): Ground connection.
If any of these connections is missing or incorrect, the stereo may not switch on.
Check that the connections are correct according to the stereo’s installation manual. If needed, the voltage can be checked with a multimeter.
2. The red and yellow wires may need to be swapped
In some cars, the positions of the permanent and ignition-switched supplies are reversed compared with the stereo’s ISO harness.
This occurs, for example, on some older Volkswagen and Saab models.
Many car stereos therefore have quick connectors on the red and yellow wires that allow the connections to be swapped.
If the car’s connections are reversed, the problem may be resolved by reconnecting the wires according to the installation manual.
3. The car may not have a conventional ignition-switched supply (ACC)
Many modern cars use CAN-bus to control various functions, including when the car stereo switches on and off.
This means there is not always a conventional ignition-switched 12 V connection in the car’s factory connector.
In these cases, you may need:
A CAN-bus adapter that generates an ignition-switched signal for the aftermarket stereo.
A separate ignition-switched connection from a suitable circuit in the car.
The solution that works depends on the car model and the stereo being installed.
4. Check the connections on the stereo’s wiring harness
Some car stereos, including models from Alpine and JVC, have separate quick connectors on the red and yellow power wires.
Check that these connectors are correctly connected and that neither wire has been left disconnected.
Some harnesses allow the power supply wiring to be changed. Always follow the wiring diagram for the particular stereo model.
Please note that the red and yellow wires should not normally be joined together unless the manufacturer explicitly states that this is permitted. Incorrect wiring may leave the stereo switched on when the car is off, draining the battery.
5. Check the fuses
If the stereo still will not switch on, check the fuses.
There may be a fuse:
On the back of the car stereo.
In the car’s fuse box.
On a separate power feed or in the installation wiring harness.
If a fuse has blown, replace it with one of the same type and amperage rating.
If the new fuse also blows, the cause must be investigated before using the stereo again.
6. Check that the correct installation wiring harness is used
The car’s factory connector does not always fit an aftermarket stereo directly.
Depending on the car model, a vehicle-specific ISO harness or CAN-bus adapter may be needed for the stereo to work correctly.
An incorrect or incompatible harness may prevent the stereo from receiving the correct power supply.
What should I do if the car stereo still will not switch on?
If you have checked the power supply, ground connection, fuses and wiring harness without finding the fault, we recommend having the installation checked by a qualified installer.
Contact our customer service team or visit one of our stores for help. Provide the car’s make, model and model year, along with the car stereo you are trying to install, so we can help you find the right solution.