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

PaulHunt73 paulhunt73 at virginmedia.com
Fri May 27 01:55:14 MDT 2022

The wire is smoking because whatever it's feeding is shorted to earth, 
so you will have to follow that wire to the radio.  If you have a fuse 
in the wire going into the radio then it's not the radio itself or that 
would have blown.  Assuming there IS a fuse in there and not a nail or 
something.  If no fuse then it could be the radio so disconnect it and 
try again, and if it still smokes the short is between that point and 
the visible melting of the white/green.

It's not the switch that is faulty in this respect, although having been 
feeding a short-circuit the contacts in the switch may have been 
damaged.  It does sound as if the switch is iffy as well, maybe because 
of the short having been present in the past. So you need to find and 
fix the short before changing the switch or you are likely to damage 
that switch as well.  That wire should only go from the switch to the 
centre console for the radio ending at a bullet connector, it doesn't go 
via the engine compartment.


On 25/05/2022 01:52, Steve Shoyer wrote:
> 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.
> Thanks.
> --Steve (1980 MGB)
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