Basically, one must view the current flow and separate the circuits involved until the culprit is identified.

More specifically, the current should be less than 50ma probably closer to 25ma, at rest with all control units asleep. Here, though lies the greatest difficulty. To get ammeter readings in that range one must be in series with the circuit. Since the circuit isn't known one must start at the battery and separate circuits elsewhere. Another problem exists due to the way the ammeter is inserted. To do it properly the ammeter must be inserted without disconnecting the circuit. Disconnecting the circuit in effect reboots the control units and can easily change the test results.

A suggested mechanism is to get a battery disconnect switch installed on the negative terminal of the battery. Run the ammeter circuit across the future open circuit (the disconnect carries the heavy loads and allows all operation and then disconnects the circuit usually with a rotary switch). Run the vehicle normally and when the igntion has been switched off the disconnect is openned. The minor currents still operating now flow through the bypass ammeter circuit. These currents could easily be in the 100ma or more range until all control units go asleep. The sleep function should take place in a few minutes.

Once the current is stable, the decision is made whether it is too great and to divide the involved circuits to find the defective one. Remember that interior lighting circuits in late model cars can take over an amp (1000ma). Most ammeters have fused circuits at about 2a (2000ma), anything left on will likely blow the ammeters internal fuse.

The easiest way to separate the circuits is to pull fuses. Eventually a power distribution tree should be viewed to be sure the separation is complete.

Go get em.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician