[Mgs] 1980 MGB wiring question

PaulHunt73 paulhunt73 at virginmedia.com
Tue Aug 10 03:43:29 MDT 2021


The horn wiring changed on late model cars so that the stalk button puts out 12v to the horns, and the horns only have one wire each as they pick up an earth from their mountings.

As such the horn push should have purple (12v, fused always live) and purple/black (to the horn) wires.  First thing to check is, does the interior light work? If not maybe the purple supply from the fusebox has failed, bottom fuse.

If so, with it lit press the horn button.  Does it go out?  If so then there is a bad connection back through the fusebox.

Next it depends on whether it is easier for you to check the wiring at the multi-plug by the column, or at the horns.  In the former case look for the purple and purple black wires and check them (connector still plugged together) for 12v on the purple all the time, and on the purple/black when the button is pushed.  If on the purple but not the purple/black the switch or wiring in the stalk is faulty.  Sometimes the wires are moulded into the connector blocks so you can only test by parting the connectors just enough to expose the pins, but they are still making contact.

At the horns with the button pressed you should have 12v on the purple/black spades on the horns (wiring connected).  If not and the test at the column multi-plug was good then the circuit back to there is faulty, most likely is a bad connection between the wiring connector and horn spade.

If you see 12v on the horn spade check a clean part of the horn body for 12v as well. If you see that then the horn earthing is bad.  If you saw 12v on the purple/black spade but not on the body then the horn is bad internally.

It might seem unlikely that the fault is at the horns in both cases, but anything is possible.

BTW stuff the trumpets with rags to avoid getting a loud blast if you disturb the fault and one or other should suddenly start working :o)

PaulH
  ----- Original Message ----- 


  We’re working on a 1980 B with a maddening assortment of electrical problems.  Right now we’re trying to figure out why the horn push won’t work—and all the wiring diagrams (Bentley & Advance Autowire)—show the horn as having purple wiring—apparently meant for the  horn push in the steering wheel button, not the push-in-the-wiper-stalk of this car.  Any advice from the List?
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