An amp meter is used to quantify amperage... Like when you want to figure out what resistance you should use, or how much power you need to drop. It's useful for finding watts as well.



A light tester is used to validate current draw. This is what we're trying to do here.



I recently found that out of 10 multimeters in my shop, 5 had bad amperage fuses. That's a shop full of electronics technicians, people who know the proper usage of the amperage mode. They still blew the fuses. The Fluke multi-meters we use had no indicator that the amp fuse was bad either. Each multimeter just read 0A when connected to a current source.



A light tester is a simple tool and much more suited to finding current draw then a multimeter which is designed to enumerate current draw. Most people have a small 12V lamp somewhere so that makes testing with a light very easy if you don't have a light tester.

 

. . . and if your lamp has a bulb that won't light up with the amount of current that is draining his battery, it is good for nothing. It is simplicity itself to test and see if your multimeter is functional when reading current. Put a 100 ohm resistor in series with it across the battery. If it shows current, it works. There is zero harm going to come to a multimeter with a 20, 10, or probably even 2A range when checking for a small current draw with the car off.