I am sure there is constant 12V on the line, though the empeg stops immediately; led goes out and harddisk stops abruptly

This sounds like your 12v is NOT permanent. This shouldn't happen unless the empeg receives no power at all.

How about when you put the empeg into the sled while the engine is off; should the empeg power on?

If I recall, mine powers up for a second (I think I see the logo, etc.) and then goes back to sleep mode. I'll post an edit in a half hour or so when I go home.

-Trevor

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Mk 2, Green 12GB 080000349