Thanks - at least I now know that I didn't do something funny to it when I did the install.

Actually, it sounds like you did do something funny.

If you've got a Mark 2, it should not try to boot until after you start the ignition. If you plug it into the dash, it should be dead as a doornail until you turn the key.

If it boots when you first plug it into the dash, that means the power-on-sense lead is connected to constant power instead of to the ignition-switched power.

Do you, by any chance, happen to drive an Audi or a VW? It might be the ISO-connector swapped-wires issue.

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Tony Fabris