Using a meter in the Volt setting:
1. Put a volt meter between the negative battery cable end and the Negative battery terminal (of course with the neg disconnected)
2. If the meter ( 20 volt scale) swings / shows the wrong way or - volts , swap the meter leads.
3. Next if the meter reads 12 volts , you have a drain , pull fuses till the reading is 0 volts.
4. Radios that have memory of stations and clock draw 1. volt to max1.8 volts
5. If all is still 12 volt with all fuses pulled, the main wires from the Alt would be the last to pull. If you find that the Alt is the Bleed out. You have a leaking Diode.
Using a meter in the amp setting:
1. Disconnect the battery positive lead.
2. Connect the digital multimeter between the battery positive lead and the battery positive terminal.
3. Select the multimeter to the ammeter function and turn the meter ON.
4. Check the multimeter reading less than 65mA (.065 A). That's your discharge rate and is normal for most cars with radios.
5. If the discharge rate is greater than 6mA, start removing and then re-installing fuses one at a time. When you remove each fuse, write down how much the discharge rate of the battery decreases.
6. After that, try removing and installing relays one at a time and write down how much the discharge rate drops for each relay.
7. Once you've completed this, identify all of the locations where you saw a significant decrease discharge rate. Using the factory wiring diagrams if necessary, determine all components supplied by those fuse/relay locations. Disconnect components from those circuits one at a time until you identify which one is the cause of the high current draw (as indicated by the ammeter).
What is the difference? Only thing is using the Volt (neg terminal process) protects your multimeter better.