Danny D. has written on 2/1/2014 10:45 PM:
On Sat, 01 Feb 2014 05:17:38 -0600, Capt Rick wrote:

No need to sacrifice a USB cable.
Measure the current going into the
cigarette lighter adapter.

Now why hadn't I thought of that!

I can just hook an ammeter across the fuse
for the cigarette lighter socket, which
will give me the current being consumed
with, and without the phone being charged!

(If you hook it across the fuse, you won't get the current you want.
Remove the fuse and connect the ammeter to the fuse terminals.)