[Mgs] 80B, melted white-green wire from ignition switch

h.duinhoven at planet.nl h.duinhoven at planet.nl
Sat May 28 02:43:13 MDT 2022

Hi Steve,


The burnt wire only is a feed to the radio - see this part of the diagram.


It seems, that the radio itself is making a short to ground. 

Pity two ignition switches have been damaged by this.


The problem with MGB’s is that many parts of the wiring are poorly protected against short circuits.

Another radio is easy to find I think.

If you want to preserve the radio because of originality, it should be repaired.


Hope this helps.




71 BGT




-----Oorspronkelijk bericht-----
Van: Mgs <mgs-bounces at autox.team.net> Namens Steve Shoyer
Verzonden: Wednesday, 25 May 2022 02:53
Aan: mgs at autox.team.net
Onderwerp: [Mgs] 80B, melted white-green wire from ignition switch


Hi - the radio in my 1980 MGB had been flaky for a while.  It would work with the key in the accessory position but not in the run position.  I could wiggle the key backwards and the radio would come on, but if I wiggled too far the engine would turn off.  I assumed that the ignition switch wasn't positioned properly but as long as I could get it to work I forgot about it by the time I got home.


Until the radio wouldn't work at all.  No power was going to it. I tried to trace the white-green circuit and found that the white-green wire was melted about 2" from the ignition switch harness connector and the insulation had bonded the white-green to the other wires in the bundle. The other wires didn't seem to be damaged, and I was able to peel the wires apart without any problem.  I repaired the burned section of white-green and tried it again, this time resulting smoke coming from the steering column.  The white-green wire had melted along most of its length.


I had a spare ignition switch (not sure of its history, but maybe it came from a parts car) and swapped it in.  Strangely, it had a splice on the white-green wire near the connector.  It also started smoking.


I tried to check the old spare switch (before it melted) to see how the switch worked but I didn't learn anything.  I also tried to see if there was voltage on any of the wires in the connector that mates with the ignition switch, thinking that power comes into the switch on the brown wire and is distributed to the other wires depending on the switch's position.  I grounded the black lead of my multimeter to the chassis and started looking for DC voltage on the other wires.  At first I didn't see anything, but when I touched one of the wires (I think white-red) the starter kicked in.  I stopped there.


Any ideas as to what might be causing the wire to melt?  I didn't see any obvious problems with the wiring harness in the engine compartment, but it's very possible that I missed something. Also, when replacing the ignition switch, should I get an aftermarket switch or the Lucas switch?  The Lucas switch is about twice the cost of aftermarket so I'm leaning toward the aftermarket switch, especially if it might just burn up as soon as it's installed.


Another odd thing is that the car ran fine when the radio wasn't working at all.  I didn't get smoke from the wiring, although by then the white-green wire was burned away before it left the ignition switch harness.




--Steve (1980 MGB)




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