My Horn Relay Isn't Working
Troubleshoot the horn circuit on your FINCH II display, whether it's a new installation or an in-service failure. This guide covers all versions of the FINCH II display.
Reference Manual
See the TPM 010 FINCH II Installation and Operation Manual and the diagram below for guidance.
Wiring the Horn
Follow the instructions below for horn installation, or skip to the next step if the horn is not installed.
- Wire from RELAY 3-4: RELAY PWR (4) to RELAY 3-4: RELAY4 COM (3).
- RELAY 3-4: RELAY4 NO (1) to HORN (+).
- RELAY 3-4: RELAY GND (5) to HORN (−).
Two Kinds of Problems
The troubleshooting steps are slightly different depending on whether the horn was working well and then quit, or is newly installed. An in-service failure is easier to troubleshoot — it was working before, and then something happened to it. Installation problems may require more in-depth troubleshooting.
Troubleshooting the In-Service Problem
The horn was working and then it quit. The most common reason for the horn to quit working is a loose or corroded connection or cut wire. Next is a blown fuse — remember that when a fuse blows, you are looking for a wiring problem that has shorted the horn power to ground, not a loose wire. Next is a defective horn.
To test for voltage, place the test light clip or the Voltmeter negative probe on the ground — an unpainted metal part connected to the frame of the vehicle, or the GND IN terminal on the circuit board. Probe for voltage with the test light or Voltmeter positive probe; the test light will illuminate and the Voltmeter will indicate normal vehicle voltage.
To test for ground, place the test light clip or Voltmeter positive probe on the PWR IN terminal. Probe for ground with the test light or Voltmeter negative probe; the test light will illuminate and the Voltmeter will indicate normal vehicle voltage.
- Ensure that all alarms are inactive.
- Press the Horn Relay Test button to determine if the horn is working.
- If the horn works, you are looking for an intermittent problem — usually a wire that's barely making a connection.
- If the horn remains silent:
- Check the horn fuse. If it's blown, replace it and continue to inspect the wiring.
- If the fuse is OK, continue troubleshooting.
- Check the horn wiring. You are looking for a loose or corroded connection or a cut wire.
- If you find the wiring problem, repair it and retest using the Horn Relay Test button.
- Note that the horn is polarity-sensitive with + and − terminals. Observe the correct polarity.
- If you didn't find a wiring problem, use a test light or Voltmeter to check for power or ground at each point in the horn circuit.
- Check for voltage at Relay PWR terminal-4.
- Check for voltage at Relay 4 COM terminal-3.
- Check for voltage at Relay 4 NO terminal-1. Press the Horn Relay Test button to activate the relay.
- Check for voltage at the horn + terminal. Press the Horn Relay Test button to activate the relay.
- Check for ground at the horn − terminal.
- Check for ground at the Relay GND terminal-5.
Failure of the voltage checks at the relay PWR, Relay 4 COM, Relay 4 NO, and horn + terminals indicates a defective FINCH II display.
- If you still haven't found the problem, the cause is a defective horn.
Troubleshooting an Installation Problem
This is more challenging. You are looking for something out of place — a missing wire, a connection to the wrong terminal, or a blown fuse due to miswiring. The best approach is to start with the first step of installing the horn, confirm it was done correctly, and continue checking each step until you find the error. If you discover that the horn power was shorted to ground, check the fuse and replace it if needed. Use the Horn Relay Test button to test the horn as you troubleshoot.
- The horn may or may not be a self-grounding style. Bolt a self-grounding horn to an unpainted metal part connected to the vehicle frame.
- The horn relay may not be configured correctly. Check the relay configuration using SensorLink and a programming kit.
- Ensure all fuses are in place, and especially check the horn fuse to confirm it hasn't blown.
