Topic

I'd be very grateful for some thoughts and advice on a problem that I have to fix in the next couple of weeks before the bi-annual CT.
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Actually the horn's very intermittent - just suddenly worked every now and again at random and unexpected times and now hasn't worked for a while. No pattern established so far.
The horn itself seems OK and works with a separate 12v supply.

It's an early (November 2002) TF with the Lucas fob. Lots of lurking and Googling is leading me to the Rotary Coupler or perhaps a relay on the BCU (apparently a common fault on later units) but any thoughts would be welcome and if it's one of those which would you suspect most and which is the simplest to fix?

If it's the coupler can it be something like a bad contact or do they just die and need replacing? I think I have been well warned about the airbag but any other hints would be much appreciated

Since you have 2002 model and Lucas fobs you do not have BCU (with known problems on relays), but you have MFU = Multifunction unit. MFU is more robust and relays inside fail very rarely, but it is not unknow for relay to stop working.

However, what you need to do is to make a check to see if you have problem with rotary coupler or relay within MFU. You need to remove plastic surround of steering column, especialy upper part. You need to find white connector which plugs into rotary coupler. It is 6-way connector. Unplug it. There on positions 4 and 6 you will find Purple/Black trace and Black wires respectively. You need to bridge these two wires and you will see if horn works.
If horn works MFU relay is fine and you have problem with rotary coupler. If horn does not work, you need to replace MFU unit for new one as most probably relay is packed.

The rotary coupler has 6 wires. Only 2 are used on the MGF. If one has failed causing the horn problem it is possible to use one of the others.

FYI the coupler has 3 pairs of wires for other cars in the MG Rover range that had audio volume controls and cruise control.

If the horn has been intermittent it’s unlikely to be the rotary coupler. It’s often referred to as the clock spring for a reason, it’s just that a coiled spring which winds or unwinds as you turn the wheel. If one of the ways fails & that carries the horn current, it fails, there is no half way house, Twang, no connection.
The horn didn’t work on my car when I bought it, it turned out that a relay in the MFU had gone bugger up. There is however a couple of connectors between one & the other & there is a chance of intermittentsy.
M

If your horn isn’t functioning all that well I believe that you can get some little blue pills from you doctor that will harden it’s resolve…..
Check your electrical connections and earthing, apply 12volts directly to the horn and see if it actually still works before getting anymore complicated

Cobber wrote:

<<<snip>>>Check your electrical connections and earthing, apply 12volts directly to the horn and see if it actually still works before getting anymore complicated

IIRC the horn has a constant live 12v supply with the earthing controlled by the MFU based on requests from either the horn buttons or the alarm.

Then all
Play a grounding directly to the horn to see if it works, the point is to test the horn itself, personally I remove the horn and bench test it to be sure it works before anything else it’s easier to undo 1 bolt than buggerise about pulling steering columns apart to get at clock springs or cracking open control units to check relays.

Another vote for testing the horns. I was so convinced that the electrickery of relays and clock springs were to blame until I did check the horns themselves. Both had failed and a pair from Darren sorted it.
The only irritation is that the horn contacts are tiny.

Has the mystery of the french horn been solved.