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

Steve Shoyer steve at shoyer.com
Tue May 24 18:52:48 MDT 2022

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 

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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