307
Horn fault causing an MOT failure
One of the MOT tests is the correct functioning of the horn and at an annual test recently, Victor Smith (Harvest Gold 1089) was sad to see no hoot came when the horn push was pressed by the MOT examiner - but why? This brief note explains how to solve the problem. (Jul 04)

As the examiner worked his way methodically through the MOT checks, he got to the stage of sitting in the cockpit and checking the function of the side and main lights, indicators and stop light, washers and windscreen wipers and then pressed the horn push - silence, or rather a very, very weak "oink"! My immediate thoughts were "Oh crumbs, it's finally decided not to work!". Yes for some time it had on just a few occasions not hooted on being pressed and it had become one of those jobs I had said to myself "I really must check that out and put it right" but didn't. Well now I had to sort it out.


Brush or sprung electrical contact pin (BHA5041)


I pulled off the horn push (BHA5135) and there sitting in the middle of the slip ring (BHA5042) was the brush (BHA5041). The MGBGTV8 parts manual (AKM 0039) says "brush" but a more descriptive name might be "sprung electrical contact pin" - it's a telescopic device which makes a contact to earth when compressed by the action of pressing down on the horn push, when of course the horn should sound as the electrical circuit is made. So I pulled the brush out and peered down into the recess and saw at the bottom a small accumulation of black gunge where the bottom of the brush should make an electrical contact. Selecting a fine screwdriver and a thin wrap of kitchen paper, I reached down with a few gentle twirls and on examining the paper a good wipe of the gunge had been recovered - and even better, a peer down the hole revealed a clean recess. Reassembling the brush and popping the horn push back on and to my delight a full bodied "parp" from the horn!

On the MOT re-test it sailed through. I now feel like Toad in Wind in the Willows - hoot, hoot! But no I haven't used the horn at all since leaving the MOT test station, and in fact have rarely done so over the 30 years I have had the car! This is not a very technical note but it may just help a member who finds his car struck dumb one day!


Footnote for overseas members: the MOT Test (Ministry of Transport) is the mandatory annual test to ensure a car is roadworthy before a UK road fund licence can be issued permitting the car to be driven on the public roads in Britain.

Copyright reserved by the V8 Register