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MG TD TF 1500 - HORN RELAY

Hi Guy's I have a problem with my horn button on my 1953 MGTD It's the later type push button without the dip swithg included. It works intermitently, and sometimes not at all. It is definately horn button related as the horns work fine,when tested off the car. My car is positive earth and I think the horn is unable to cope with the current attached with earthing through it's contacts. I think a relay would be the answer to all my problems. But which type would I use and how would I wire it in. Over to you Guy's.
Jack
Jack N Martin

Jack,

The horn button on a TD is as robust as any relay. Usually the relay on a British car is used on the horn if it has a stalk mounted horn button (those tend to have smaller contacts) or if it is felt that it would be better to bring the current directly to the horn. In this case, it would be better to disassemble the switch, clean the contacts, check the spring action and reassemble. However, if you want a relay:

The terminals on a relay or 85-86 the actuating terminals from the low current source or switch, and 30-87 the high current terminals which are activated when the low current powers the coil which closes the high current contacts. Sometims there is an 87a which would power a second circuit, and there are relays that have a set of contacts that are energized with the relay off and a set of contacts that are energized with the relay on. You can't go too wrong with a 20 amp four terminal relay as it will wire as follows.

To wire your relay trace the purple with black wire (early car) or Brown with black wire (later car) from your horn switch, before it goes to the double connecter behind the dash. separate the wire going into the double connector and run that end to the relay termainal 86, and then provide a 12 volt source to the terminal at 85. It can be a light gauge wire coming off your inspection socket, or any solid purple (early) or solid brown wire (early or late). Connect a wire from the double connector that goes to the horns to the 87 terminal on the relay, and connect a good ground to the 30 terminal. If your horn switch will pass any minimal amount of current your horns will work.

warmly,
dave
Dave Braun

Had horn problems like you describe . Horns worked, button worked, until you put it all together. Finally traced it to a poor connection of the horn circuit at the voltage regulator. Cleaned and tightened .... works fine now.

Its an easy fix, might be worth a look.
C.R. Tyrell

This thread was discussed on 23/12/2011

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