Stu,
I suspect that nothing like 55 amps was being drawn. As you point out,
there would have been lots of smoke. It appears that there was not a real
solid short so that no damage perhaps occurred, but yet there was
sufficient current leaking to run down the battery. I suggest you check the
wiring from the battery to the ammeter and make certain it corresponds to
the workshop manual drawing. Also check the wiring to the voltage
regulator.
When I purchased my TF, some previous owner or mechanic had wired a
device to the input side of the ammeter. Combining this problem with a
mis-wired voltage regulator caused all kinds of wild readings. Correcting
the regulator wiring and moving the device connection to the downstream side
of the ammeter solved the problem. With the horns and starter not being
operated, the wire from the battery to the ammeter on the TF should be free
of any other connections. Ignoring wire resistance, the electrical loads
should be downstream of the ammeter (aside from horns and starter).
I would also suggest that you put in a complete set of fuses to protect the
wire to all circuits. As you are perhaps aware, some of the light circuits
have no fuse protection. In other cases, wires will burn up before the
heavy original fuses blow. On my TF, I installed a fuse box under the dash
on the back of the tool box, and have fuses for thirteen different circuits.
Each fuse is tailored to the wire and device being served.
Ben
54 TF 1500
---- Original Message -----
From: Stuart Keen <simbafish@home.com>
To: MG T Digest <mg-t@autox.team.net>
Sent: Saturday, August 26, 2000 12:48 PM
Subject: Electrical Short
> 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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