Originally Posted by
mudnut
An alternator really needs 1500 or so revs to get charging, then will charge at idle. On my old Trol, its easy to check for parasitic draw. With the ignition off just disconnect the battery negative and clip a multimeter in series with it on 10amps. My Q draws a few hundred milliamps for a few seconds to power up the clock, etc. It then dies down to a miniscule amount.
The alternator should put out between 13.8 to 14.3 volts a bit of time after cranking the starter. Even with lights on high and accessories going at 1500 rpm it should stay steady.
On newer vehicles, checking for parasitic draw becomes problematic, as the ECU transmission control, body modules etc all draw a small amount. And its not good to disconnect the battery without a smaller battery to keep voltage present.
If you find that the parasitic draw is high, before diving too deep and pulling wiring apart, you can pull fuses and relays to see if it drops.