>Er, Dave - I've never seen any kind of an AC component on
>that lead. Typically on my test rig (fancy word for a
>lash-up of motor and meters) all that signal does is sit @
>12 volts when connected to a lamp and the alternator is at
>rest, then it drops to zip and sinks 12 volts when the
>alternator kicks over. I will admit I've never had a scope
>on it, but high-resistance voltmeter should have shown a
>pulsing DC or AC component.
>
>The thing that mystifies me is that if there was any kind
>of RPM-dependent signal on that lead the bulb on the
>circuit would glow - perhaps dimly, but you would see
>illumination.
>
>You sure we're talking the same setup here?
>
>
Yes.
I did some digging, and found an FW murphy tach installation bulletin
that suggests that the 10si produces 14 pulses per revolution. At
twice engine speed, that's about 175 or so pulses per second, at
idle. I don't think an incandescent bulb would notice --
particularly if the swing isn't from 12 to 0 VDC, but 12 to 6, or
something like that. I've never fiddled with putting one on a scope;
i've just hooked the things up.
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