In general, an ammeter needs to be installed between the device providing electricity and the device(s) using electricity. This kind of connection, where you break the wire and install the meter across the break, is called a "series" connection. In an automobile, the ammeter should be installed in the smaller of the two positive (usually red) battery cables, the one that runs from the positive battery terminal to the alternator charging terminal (and also to rest of the non-starter electrical loads). Here is a simple drawing: B+ ------(\)---------- A+ ---------- ACC
ST Where: (\) = The Ammeter
B+ = Positive Battery Terminal
A+ = Alternator Charging Terminal
ST = Starter (large cable)
ACC = To vehicle Accessories (small cable) i.e., ignition, lights, etc.
------ = smaller (typically 10 gauge) red wire
= larger battery/starter cable (typically 4 gauge or larger) Notes: * Do not install the ammeter in the large cable that goes to the starter. * The small cable from the Alternator to the battery may be attached to the battery terminal, or it may be attached to the starter terminal. Electrically these are equivalent. * In order for the ammeter to properly show whether the battery is charging or discharging, the ammeter must be installed between (a) the battery and (b) both the alternator and fuse block/ignition switch. * If the accessory cable is also attached to the starter, it will have to be removed and attached to the alternator side of the ammeter or to the alternator as shown in the drawing. * Make sure you disconnect the negative battery terminal before working on the electrical system. ALWAYS wear safety googles whenever working on or near the vehicle battery.