I have just returned from the superb NEMGTR Great Circle tour - 5,300
total miles in a 1951 MGTD MkII (tour around 3 of the Great Lakes was
2,400 miles, the rest was getting from Florida to Ste Catharine and
return from Cleveland). On my way to Green Bay, WI, Lucas (or is it
Murphy) made me aware that he was ever present.
Driving during the day in the rain, I had the lights on. As I motored
along, my TD finally died. I was able to restart it after a short rest,
but had to keep the lights off. In Green Bay I discovered the socket for
the license plate light had shorted to ground. I made the rest of the
trip with the connecting wire disconnected.
QUESTION: Why did my wire harness not burn up? Where did all the current
dissipate? Just before the trip, I had replaced the defective 30 AMP
ammeter with a 60 (not 30) ammeter. I did not notice when I was driving,
but at the motel, observed that the short was pulling 55 AMPS!! I have
looked at all the readily visible cable and cannot find any charred
wires (another TD on the trip had a problem with his wiper motor and the
cable to the wiper COMPLETELY burned up (smoke and small amount of
flames).
I thought the ammeter was superfluous. As long as the red ignition light
was not lit, then the battery was charging okay so ammeter not really
needed. Now I find there is a more important reason for the ammeter. It
will tell you when there is a short!! Unfortunately, during the above
incident, I did not notice the response on the ammeter (meter hidden by
the steering wheel) and drove the TD until the short eventually drained
the battery and stalled the car.
I hesitated to use the lights after this electrical short incident, but
with approx a week left, there were times I could not avoid using them.
On my return to Florida, in a torrential thunderstorm in Ohio, I had the
lights on for two hours. I constantly watched the ammeter for any
indication of burned wires shorting, but all seems to be okay. So why
did the wires not burn with 55 amps going through them (actually
probably more like 70 AMPs as the generator output is approx 15 amps
that was trying to offset the negative pull).
Stu Keen
Venice, Fl
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