Battery drain test procedure question

[Multibeemer]

This may be a dumb question, but I'll ask anyway. I think I may have a battery drain problem, so I want to test the amount of parasitic current flow in the car's electrical system. The procedure as I understand it is to disconnect the positive battery cable, and attach the positive (red) lead from an ammeter to the positive battery post, and the negative (black) ammeter lead to the battery cable I just removed. My ammeter only goes up to 250 mA, but my car violently pegs the needle, indicating I have a large leak.

However, here's my question. Since the X5's battery is located under the luggage area, I have to open the rear hatch to get to it. So, when I connect an ammeter across the battery post and lead as described above, doesn't that complete the circuit and attempt to engage all the interior lights that come on when you open the hatch? Or is the ammeter's internal resistance high enough to prevent that? If this is a problem, how does one actually test the current drain on a car such as the X5, whose battery is located in the interior of the vehicle? Thanks.