Originally Posted by cotenseto
Why would there be an intermittent, variable spike in amperage above 15, that BMW knows about? If that's a normal condition, they should have put in the 20A from the beginning. Kinda stupid. Does anyone know an easy way to test the amperage draw on the actuator with a multimeter DIY?
Assuming your meter has a fast enough transient response to see the real peak value, you can do this two ways depending on how you feel. one way keeps protection in the circuit, one way doesn't.
If you remove the fuse that controls current to the actuator and use the meter's probes putting them where each blade of the fuse would insert into the holder you can get a current measurement when you energize the actuator. However if you are getting an excessive spike this could be bad as you have no fuse protection (aside from what's in your meter if applicable).
Another way you could do it is to buy a blade fuse holder that has a "pigtail" or wire leads coming off of it. one lead you would put into the fuse holder where a blade of the fuse would go, one probe goes into the holder where the other blade would go, and the extra wire connects to the extra probe to complete the circuit. You can then energize the actuator and get a current measurement.
When you want to measure current in a DC circuit, you want the meter to be an element that is in series with the rest of the loop you are testing. When you want to test voltage, the meter becomes an element that is placed in parallel across the element you want to test.