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MG MGB Technical - radio

my radio and horn suddenly quit working, are they on the same circuit. 1974 chrome bumper car.

Thanks
rick baranyi

They shouldn't be on the same circuit but you'll need to verify that since your radio may be an after market addition. The horn is on the purple circuit which is always hot. The radio should be on the accessory circuit from the ignition switch.

Go to http://www.advanceautowire.com/mgb.pdf and select the appropriate wiring diagram. Have it enlarged and laminated. Than you can use a dry erase marker to trace the circuits you are working on. You wan't regret it.
Dan Hiltz

The horn circuit is a long, permanently live one, actuation is by earthing/grounding at the wheel boss. It is on there same circuit as the interior and courtesy light. If they are still functioning the problem might be at the steering wheel, if not check the "bottom" fuse.. There's a brass ring on the back of the wheel which is in "wiping" contact with a sprung copper contact. Check that.
The radio "should", fed by a green and white wire which is made live at the first click of the key. It often also has an in-line fuse, and many radios come with fuses on the live in side, often two. BUT people often wire the radio to be always usable, ignition on or not. In which case it will be fed off the purple circuit also.
Allan Reeling

" If they are still functioning "

If the courtesy lights work then with them on operate the horn button. If they go off then the problem is at the fusebox.

If they stay on and the horn doesn't sound then there is a break in the horn circuit itself.

See if you have 12v on the purple/black feeding the horn push. If not then check at the horn terminals themselves, it should be on both of them i.e. the purple from the fusebox and the purple/black from the horn push.

No 12v on either means the problem lies back towards the fusebox. On the purple but not the purple/black says the horn itself is faulty.

If on both see if the purple/black drop to zero when the horn push is operated.

If it doesn't then there is a break back through that circuit and the horn/push.

If it does, and the 12v on the purple has also gone, then the problem lies back towards the fusebox.

If there is still 12v there then the horn is faulty.
Paul Hunt

This thread was discussed between 26/03/2014 and 27/03/2014

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