How to Properly Connect a Car Radio ISO Connector

car radio - ISO connector wiring diagram

When installing a new car radio or replacing your old one, one of the most important steps is connecting the ISO connector properly. The ISO connector is a standardized plug that makes wiring your car stereo much simpler and safer. It links the stereo to your car’s power supply, speakers, and antenna functions.

While wiring can sound intimidating, connecting a car radio ISO connector is actually very straightforward if you follow the right steps. In this guide, you'll learn how to wire it correctly so you can enjoy your new stereo without issues.

Or you can watch the video instead :)

What Is an ISO Connector?

Before we dive into the steps, let’s quickly clarify what an ISO connector is.

An ISO connector is a pair of rectangular plugs used in most car audio systems. These plugs allow the radio to connect to your car's wiring without cutting or modifying the original cables.

  • Block A (Power): Power supply, ignition, ground, antenna, amplifier signal
  • Block B (Speakers): Connections for all front and rear speakers

Most modern cars already include an ISO harness. If yours doesn’t, you can use a vehicle-specific ISO adapter.

What You’ll Need

Step 1: Disconnect the Car Battery

Safety first.

  1. Open your car’s hood
  2. Remove the negative terminal (-) from the battery
  3. Set it aside where it cannot touch metal

This prevents short circuits and protects the stereo.

Step 2: Locate the Car’s ISO Connector

Behind the radio slot, you should see the factory ISO harness.
If you're replacing an old stereo, simply unplug it.

If your car doesn’t have ISO:

  • You need a vehicle-specific adapter (cheap and widely available).

Step 3: Connect the ISO Plug to Your Car Radio

Most radios come with two ISO plugs already attached.

Block A — Power Plug

Typical wire meanings:

  • Yellow → Constant 12V
  • Red → Ignition/switched 12V
  • Black → Ground
  • Blue → Antenna or amplifier signal

Block B — Speaker Plug

Color pairs for:

  • Front left
  • Front right
  • Rear left
  • Rear right

Each speaker has a + and – wire.
The connectors fit only one way—insert until they click.

Step 4: Double-Check the Wiring

Even though ISO is standardized, always verify:

Power wires

  • Yellow → 12V constant
  • Red → 12V ignition
  • Black → Ground
  • Blue → Antenna/amp (if used)

Speakers

Ensure left/right and positive/negative pairs are matched correctly.

Incorrect polarity won’t damage anything but weakens bass and clarity.

Step 5: Secure the Connections

  • Make sure all connections are tight
  • Insulate exposed wires if you spliced anything
  • Avoid loose connectors—these cause intermittent power or audio issues

Step 6: Reconnect the Battery & Test the Radio

  1. Reattach the negative terminal
  2. Turn the ignition on
  3. Power up the stereo
  4. Test all speakers
  5. Check FM/AM signal (antenna working?)

Everything functional? Continue.

Step 7: Install the Radio

  • Carefully push wires into the dashboard
  • Slide the stereo into place
  • Secure with screws or the supplied mounting sleeve
  • Reinstall dashboard trim

Your ISO-connected radio is now ready!

Final Tips

  • Use color-coded diagrams from your car manual or radio instructions
  • Avoid cutting factory wiring — always use ISO adapters
  • Check antenna and ground connections if reception is weak

Want to learn how to connect speakers? → HERE

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