I have discovered that the horn does not work on my wife's MG TF.
The car passed an mot in march so it must have worked then, have checked fuse, ok.
Is this a common fault on this car? Is there a way to test the horn itself?
Any advice welcome.
First it is important to know what kind of fob/remote you have? Oval with logo in the middle?
If this is correct, then problem might be in the failed relay within SCU unit.
You can test the horn with additional wire from the battery and by that get 12V to horn inmorder to see if horn is working or not. If horn is working then most probably cause is relay within SCU unit.
Wow, that's great a reply so soon. The fob has three buttons on it mg logo in middle.
At present I do not have a wiring diagram for this car, is the relay located in the drivers side footwell near the steering wheel?
No, the relay is soldered on printed circuit board of SCU unit. That is black box behind centre cosole which you would need to remove, open, check resolder. Look into the thred which is linked for more detailed information.
Unplug the alarm, apply 12v to one contact and earth the other.
You can test the operation of the horn when triggered by the alarm by setting the alarm, open the boot which doesn't trigger the alarm, and pull the release for the bonnet, the horn should sound.
You will of course need a soldering iron and either a desolder braid or desolder pump as they are soldered to the printed circuit board The first post on the thread Roverlike linked to will tell you which relay operates the horn.
Did you check the horn wasn't faulty first? I know others have asked but your posts don't indicate you have. In all honesty though I'd assume its the pektron relay. My brothers one had a by-pass with two separate relays and a button as the relay was gone. He also did all 5 relays as he had it apart rather than just the one.
You might find watching this youtube vid may help guide you doing the replacement:
It relates to a ZR (but the Pektron unit is identical), so you can ignore the first 11 minutes - from then on it shows the dismantling of the unit, desoldering and removal of the faulty relay, and fitting of the new one.
You will also need a 5 point security Torx bit to undo the screw on the cage which holds the unit behind the dash. Tecnozen can supply one if needed.
Youtube vid was not showing properly so I fixed that.
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