Relays are typically the most reliable moving part in a vehicle's electrical system and seldom require replacement. When one does fail, though, replacement is very easy in most cases. Before replacing a relay, test the relay with a multimeter to properly diagnose the problem. A horn that's not working may be caused by a bad relay, a broken wire, a broken horn switch, or even the horn itself may be to blame, so troubleshoot thoroughly before replacing any parts.
Locate the horn relay. On most Mitsubishi Montero model years, the horn relay can be found at the fuse box under the hood. The relay's position in the fuse box will be noted on the fuse cover.
Open the fuse cover. Verify the position of the relay in the fuse box using the diagram on the fuse cover. Use a 90-degree pick tool to remove the relay, if necessary.
Inspect the relay terminals for dirt and corrosion. Clean the terminals with electrical contact cleaner if needed. Examine the relay for any signs of damage.
Place the new relay into the relay socket. Have someone press the horn switch and feel the relay for movement. A properly functioning relay will produce a click that is easily felt and heard.
Replace the fuse panel and close the hood. The horn relay installation is complete.
