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15 Posts
Discussion Starter · #1 ·
2002 MG TF 135

Car is new to me and has a horn rigged up using a press button and an alternative connection to get through the MOT. (Horn itself works fine)

With the correct horn connection:
the horn from the steering wheel is inoperative
setting off the alarm causes a single beep from the horn (it doesn't repeat)

I have checked the continuity from the steering wheel through the rotator and the only effect when shorting post rotator connection or pressing the horn button when assembled; is a faint click from the relay located in the internal fuse box.

Because the horn doesn't operate via horn or when alarming I assume it is an issue common to both cases - but what or where is it?

Is there a commonality in the Lucas 5SA?
Where is the common earthing point? (I can't determine from the wiring diagrams I've found).

Help please

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13,519 Posts
You alarm system use horn to provide sound when alarm is off. Horn is operated by relay which is inside Multy Function Unit bolted on the back side of the fusebox. It is red box. You need to unbolt the fusebox in order to see/reach MFU.
MFU is realy reliable unit and rarely malfunction. I would suggest to check by multimeter if relay is working as it should while you might hve problem elsewhere along wires. Or you need to replace MFU.
If only horn is not working, then I would not suspect any earth point is in question.

15 Posts
Discussion Starter · #3 ·
Thought I'd already said thanks - but hay ho.
Decided to acquire ano MFU rather than take old one off for testing and then taking action.
So that's on order and I'm busy for the next 2 weeks - so I'll come back then.
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