Ferrari 550: Reverse lights not coming on - diagnosis

I noticed that both reverse lights on my 550 were not turning on. I want to write a short diagnostic guide here for others to find when they search this forum.

Here are potential causes of the lights not coming on, from easiest to hardest to fix:

Burned out bulbs
If only one of your lights are dead, replace the bulb. You can find instructions on how to do this in the user manual (page 5.14).

If both lights are inoperative, it’s likely that the cause is something else.

Reverse gear detector switch
There is a switch inside your shifter gate that tells the system that you selected Reverse. You can clearly see the switch when you shine a flashlight into the gate. This switch can get dirty and stop working, or become misaligned.

Turn the car ignition on. Have someone stand behind the car to report the state of the reverse lights. With the eraser end of a pencil, poke at the switch to make it move its full range of motion. When the switch works correctly, the reverse light should come on even when the switch is only partially depressed. Pressing the switch all the way several times helps to dislodge any dirt that may have gotten into the contacts.

If you’re convinced the switch works, put the gear shifter into Reverse. In that position, it should visibly press on the switch. Verify that the light is on. If not, the switch or shifter may have gotten misaligned. Realigning or replacing the switch may need disassembly of the center console and I won’t cover that here. But at least you know what to replace now.

Pressing the switch should produce a soft but audible “click” from the passenger footwell as a relay is engaged and disengaged. If you don’t hear that sound, read on.

Bad fuse

To open the fuse box, remove the passenger floor mat. You will see a hinged metal cover held in place by thumb screws on its top. Turn the thumb screws so they are horizontal, then pull on them (I had to use pliers) until they pop out. Flip the panel down to expose the fuse/relay board.

The reverse light goes through Fuse number 3, third from the left. Pop out the fuse and check if it’s burned out. Replace the fuse if so.

Bad relay

The reverse light uses a relay at position T (third from the right, row closest to you). To test the relay, swap that relay with the one in position F (fourth from the left, next row up, next to the empty socket) which controls your high beams. Once you swap them, turn your ignition on, and flash your high beams. You should hear an audible click when you do that, and your high beams should come on. If they don’t, you have a bad relay. Also, test if your reverse lights now come on. If they do, that indicates you had a bad relay. Remember which relay you need to replace!

Replace the relay with Bosch part number 0332019103.

Hope that helps.