Horn not working
Discussion
Hi Guys,
Just got my repaired steering control ecu back because my lights did not work properly. Lights work now. Horn does not work....
I got the steering wheel off. The horn button was not functioning, but this did not let the horn come back to life, We checked the signal at the steering control ecu (the purple/black wire) gives earth when I put a screwdriver between the 2 pins in the steering wheel boss. So, the signal through the steering wheel boss, the flat cables and out off the steering control ecu does work.
I saw in my hand book that the upper right relais on the fuse box is the horn relais.
Does the purple/black wire, coming out of the steering control unit, go to the relais? and does it then send out a 12V signal to the horn? The horn has a constant earth, so I guess this must be the case?
Just got my repaired steering control ecu back because my lights did not work properly. Lights work now. Horn does not work....
I got the steering wheel off. The horn button was not functioning, but this did not let the horn come back to life, We checked the signal at the steering control ecu (the purple/black wire) gives earth when I put a screwdriver between the 2 pins in the steering wheel boss. So, the signal through the steering wheel boss, the flat cables and out off the steering control ecu does work.
I saw in my hand book that the upper right relais on the fuse box is the horn relais.
Does the purple/black wire, coming out of the steering control unit, go to the relais? and does it then send out a 12V signal to the horn? The horn has a constant earth, so I guess this must be the case?
This is what AI said:
On a TVR Cerbera, the horn relay is typically located on the main fuse box, which is situated in the boot on the driver's side (behind a velcro-attached cover). The horn system often operates on a ground-trigger mechanism, where the horn push on the steering wheel acts as the switch to ground the relay.
TVR Cerbera Horn Relay Wiring & Location
Location: The horn relay is commonly the upper right relay on the fuse box located in the boot.
Relay Type: A 4-pin or 5-pin (often with 87a unused) automotive relay is typical (often brown-cased on later cars).
Typical Pin Connections (Standard 4-Pin):
Pin 30: Constant 12V supply (usually via the main fuse box/brown wire).
Pin 85: Ground trigger from the steering wheel horn button (purple/black wire).
Pin 86: 12V ignition power or spliced from Pin 30.
Pin 87: Output to the horn's positive terminal.
Trigger Mechanism: When the horn button is pressed, it sends a ground signal via the steering control ECU (often a purple/black wire) to the relay, activating it.
Common Horn Troubleshooting & Wiring Issues
Fuse: The horn fuse is often #8 (counting from the front of the car) and is shared with the courtesy lamps and cigarette lighter.
Steering ECU/Ribbon Cable: Because the horn operates through the steering wheel ECU ribbon cable (controlling horn, wipers, washers), a failure of all steering wheel buttons usually points to the ribbon cable inside the steering boss or a steering ECU issue.
Constant Earth: The horns themselves are located in the lower "mouth" of the car and often have a constant earth, needing 12V from the relay to sound.
Alternative Wiring: Some owners opt to wire in a new dedicated relay for high-power horns, using Pin 30 for direct battery feed (fused), Pin 87 to the horn, and pins 85/86 for the relay coil.
If you are losing horn function along with other steering wheel controls, inspect the purple/black wire or the steering column ribbon cable.
On a TVR Cerbera, the horn relay is typically located on the main fuse box, which is situated in the boot on the driver's side (behind a velcro-attached cover). The horn system often operates on a ground-trigger mechanism, where the horn push on the steering wheel acts as the switch to ground the relay.
TVR Cerbera Horn Relay Wiring & Location
Location: The horn relay is commonly the upper right relay on the fuse box located in the boot.
Relay Type: A 4-pin or 5-pin (often with 87a unused) automotive relay is typical (often brown-cased on later cars).
Typical Pin Connections (Standard 4-Pin):
Pin 30: Constant 12V supply (usually via the main fuse box/brown wire).
Pin 85: Ground trigger from the steering wheel horn button (purple/black wire).
Pin 86: 12V ignition power or spliced from Pin 30.
Pin 87: Output to the horn's positive terminal.
Trigger Mechanism: When the horn button is pressed, it sends a ground signal via the steering control ECU (often a purple/black wire) to the relay, activating it.
Common Horn Troubleshooting & Wiring Issues
Fuse: The horn fuse is often #8 (counting from the front of the car) and is shared with the courtesy lamps and cigarette lighter.
Steering ECU/Ribbon Cable: Because the horn operates through the steering wheel ECU ribbon cable (controlling horn, wipers, washers), a failure of all steering wheel buttons usually points to the ribbon cable inside the steering boss or a steering ECU issue.
Constant Earth: The horns themselves are located in the lower "mouth" of the car and often have a constant earth, needing 12V from the relay to sound.
Alternative Wiring: Some owners opt to wire in a new dedicated relay for high-power horns, using Pin 30 for direct battery feed (fused), Pin 87 to the horn, and pins 85/86 for the relay coil.
If you are losing horn function along with other steering wheel controls, inspect the purple/black wire or the steering column ribbon cable.
Hi there,
Pushing the button on steering wheel grounds/closes the relay. That side sounds ok from what you describe.
If the relay clicks, then your issue is with the relay or the other side of the circuit, which is the purple/white wire from connector K.
This is fusebox-dependent and may differ on later Cerbera. This circuit is annotated horn drive on the wiring diagrams otherwise. I wouldn't suspect horns themselves as they tend to be very simple things.
If the relay is ok, I would check the earth at front and then junctions/connectors on route back to the fusebox. It shouldn’t make any odds really if you do this other way round.
Hope this helps, cheers
Pushing the button on steering wheel grounds/closes the relay. That side sounds ok from what you describe.
If the relay clicks, then your issue is with the relay or the other side of the circuit, which is the purple/white wire from connector K.
This is fusebox-dependent and may differ on later Cerbera. This circuit is annotated horn drive on the wiring diagrams otherwise. I wouldn't suspect horns themselves as they tend to be very simple things.
If the relay is ok, I would check the earth at front and then junctions/connectors on route back to the fusebox. It shouldn’t make any odds really if you do this other way round.
Hope this helps, cheers
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