Dan, Nelson and interested parties---I can't get electronically
technical with you guys, but I did install my own MSD 6-A about 12 years
ago, and vaguely remember that I had an occasional run-on after turning
off the ignition switch. The instructions for "running-on" as written by
the MSD people reads as follows: (Sorry, but I don't have the means to
fax it to you)
"Running-on is a condition whereby the engine contnues to run even
though the ignition key has been 'turned off'. This condition can be
caused by one of two things:
1. The charging system leaking back into the electrical system.
2. Dieseling
Since the MSD is connected directly to the battery by the heavy red
wire, only a very small current is required to keep the ignition
energized. If the ignition continues to run after the ignition key has
been turned off, the MSD may be receiving a small current the charging
indicator. This problem sometimes occurs even on the stock ignition
systems and is easily cured by installing a diode to block the reverse
leakage current. The diode (.....then tells how to do this for separate
voltage regulators....)....and for vehicles that have the regulator
built into the alternator, install the diode in the smallest of the
three wires coming out of the alternator (normally Brown) as shown.
++++++++
Then it shows where to splice in the 1A-100V Diode between the
alternator and the charging light, by illustration.
It then covers 'dieseling' and its causes, and suggests some of the
causes and cures. Since dieseling has its own unique sound, I'm not
including their suggestions unless someone wants them later.
I'm reasonably sure I did NOT have to add the diode to my wiring, yet
have had no running-on except right after the original installation. I
don't know what may have changed around the same time, but haven't
experienced this run-on in so long I almost forgot about it. Sorry for
the fuzziness here..
It looks like Nelson did the right thing by installing the diode, and
Dan's explanation concurs. If any of you need further info, the people
at Autotronics are good about answering. They have a web site.
Dick Taylor
'73
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