When wiring a car stereo or other electronic devices in your vehicle, identifying the constant 12V wire is crucial. The 12V wire provides continuous power from the vehicle’s battery and is often red in color. However, wire colors can vary between vehicle makes and models so it’s important to verify the wire color in your specific vehicle.
Purpose of the Constant 12V Wire
The constant 12V wire, also known as the memory wire, allows your stereo, alarm system, or other electronics to maintain settings and memory when the vehicle is off. Devices connected to the constant 12V wire will remain powered even when you turn off the ignition or remove the key.
Without connection to a 12V constant power source, your car stereo would lose presets every time you turn off the vehicle. The alarm and security features on alarm systems also rely on constant 12V to sense motion and trigger sirens when the vehicle is parked.
Typical Color of the 12V Wire
Although wire colors vary, in many vehicles the constant 12V wire is red. This corresponds with common wiring standards:
- Red – Constant 12V power
- Yellow – Switched 12V power
- Black – Vehicle ground
- Blue – Remote turn-on signal
Using red for constant 12V power makes it easy to identify at a glance. However, it’s critical to verify the wire color in your specific vehicle before making connections.
Other Common 12V Wire Colors
While red is common for constant 12V wires, you may find other colors used in some vehicles:
Again, verifying the exact wire color and function is critical before tapping into any wire in your vehicle. Consult a vehicle-specific wiring diagram to be 100% sure.
How to Identify the 12V Wire
To identify the constant 12V wire without a wiring diagram:
- Turn the ignition to the “ON” or “RUN” position, but do not start the engine.
- Set your multimeter to DC voltage mode.
- Probe the wire you suspect of being constant 12V, touching the red multimeter lead to the wire and the black lead to a known ground.
- If you see approximately 12V on the multimeter display, you have found the correct constant 12V wire.
The wire should display battery voltage with the key on but engine off. When you turn the key fully to “START” the voltage may drop slightly as more systems come online.
Finding an Ignition Source
In addition to the constant 12V wire, you’ll also need an ignition source that provides 12V only when the key is turned to “ON” or “RUN.” This is required for switching on amplifiers and other devices that should only operate when the vehicle is running.
The ignition wire is often yellow or red. Use the same multimeter testing process to confirm which wire provides 12V only when the key is on, not in the off position.
Connecting to the Constant 12V Wire
Once you’ve identified the correct constant 12V wire, make your connections carefully following instructions below:
- Turn the ignition fully to “OFF” and remove the key before beginning.
- Cut the 12V wire, leaving enough room to strip and tap your new wire.
- Strip 1/2 inch of insulation from the end of the new wire.
- Crimp or solder the new wire to each side of the cut 12V wire.
- Tape up the connection using high quality electrical tape.
- Test operation by turning the key from “OFF” to “ON” and checking for 12V at the other end of the wire.
With this step-by-step process you can safely tap into the correct 12V constant power source for wiring accessories and electronics in your vehicle.
When identifying and connecting to constant 12V wires, keep these safety guidelines in mind:
- Pull fuses for circuits you’ll be working on so no power is present while testing wires.
- Never probe a wire with power present, this can damage circuits or cause electrical shorts.
- Make clean and secure crimp or solder connections for reliable performance.
- Use adhesive-lined heat shrink tubing over any exposed wire taps.
- Keep wiring away from hot or moving engine components.
- Use grommets when running wires through the firewall or metal barriers.
Installing a Fuse
It’s also critical to install an inline fuse connected to the 12V wire you are tapping into. This provides overload protection for both your vehicle’s wiring and your added electronics. Follow these steps to add a fuse:
- Select an appropriate amperage fuse based on the device being installed.
- Connect the fuse tap to the cut 12V wire before or after your new wire tap.
- Insert the fuse into the fuse tap housing.
- Test that power flows through the fuse to your device.
Adding a correctly rated fuse prevents overheating wires or damage if a short circuit occurs.
Identifying and tapping into the 12V constant power wire is crucial for installing electronics and accessories in your vehicle. While often red, wire colors can vary. Always verify the exact purpose of a wire in your specific vehicle before making connections. Use care during installation and add an inline fuse for overload protection. With these tips, you can safely tap into 12V constant power sources for mobile installs.