I don't often do amp testing when dealing with automotive circuits, other than when I perform a parasitic draw test. We'll cover that later in the article. There are two ways you can test amps in an automotive circuit. The first is with an inductive amp meter.
This is a tool that measurers the magnetic field around a wire. The circuit has to be live for this to work. Say you're looking to test the amps going to the starter via the positive battery cable. Place your ammeter around the positive battery cable and engage the starter to take your reading. You won’t get a reading if you're not cranking.
The other way to measure amps is by tying into the circuit directly, or tying in ‘series’. This means you open the circuit somewhere and insert your ammeter. All the amps in the circuit need to flow through your meter in order to test this way. This can be tricky, and many a DVOM has suffered from improper amp testing. Don't worry; most of them are fused, so if you mess up, hopefully you'll be able to replace a fuse and be back in business. So to be safe when checking high amp circuits, use an inductive lead instead of connecting in series. If you're checking for small amp values, connect directly into the circuit to take your readings. This video shows amp testing at work, as well as some other useful tests. Remember, be careful when dealing with amps.