If the diesel is wired like the sparked engines, disconnect the main cable at the jump point and measure across the new gap you create. You should not get a voltage. If you do either the alternator or the starter has a fault that’s drawing current always.

In fact if you get a voltage reading, then measure amps. If you get an amperage reading then disconnect the main cable at the alternator to measure if you can still measure voltage/current going to the starter.

Neither starter nor alternator should draw current when the engine is off but both are connected to an always live battery cable.

A draw at the starter while running should not feedback info the alternator circuit monitor so I am suspecting something in the alternator like a leaky diode allowing current to go the wrong way. Not enough to stop voltage production but throw something off.

Measuring AC on the alternator output (o-scope even better) can be very helpful. I think I'm used to seeing 400hz 0.2v ripple.

I don't think anything else is attached to that main cable so it will bea very quick test to confirm yes/no one of the two items are faulty.


–awr–

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)