Quote:
Originally Posted by undy
I won't debate this any more...
FWIW, I've got you by 10 years and have a degree in Automotive technologies.
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From a testing perspective y'all are arguing about nothing, as either way works effectively the same. The good news is everyone is correct! (Don't ya love it when that happens
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A VOM (for volt-ohm-milliampere) meter can be used to measure the open circuit (CKT) voltage when the ground wires are lifted (though this is not intuitive). The reason this works is because the ground lead on the box
floats up to the source potential if it is powered on and attempting to draw currect, i.e. to operate (recall that you need a voltage potential to be present in order for current to flow). If you read no voltage potential then the unit is not on nor trying to draw down the battery. At this point, though, you might see spurious readings, i.e. the meter might pick up electrical noise... and no, the volt meter will not get cooked.
Alternatively, you can measure the current draw directly in the ammeter mode (but make sure that you are on a high enough range setting so as not to fry the meter). Of course, if you measure current then the box is on and draining the battery.
That said, I am not familiar with the MSD box. From what I have gathered in this thread, it appears that there are two power leads to it, one switched, and one that is always on??? If that is the case, then either measurement technique should reveal some power usage by the box, though it might be quite small when in standby mode, i.e. engine not running and ignition off. Sorry if I misunderstand how the box works.
Good luck!