Ammeter

Ammeter:

Meter Scales:

An ammeter is used to measure current flow (amperage) in a circuit. Amperes are units of electron flow which indicate how many electrons are passing through the circuit. Current flow in a circuit is equal to the circuit voltage divided by total circuit resistance.

At normal operating voltage, most circuits have a characteristic amount of current flow, referred to as normal current draw. Current draw is measured in amperes (amps) with an ammeter. Comparing measured current draw with the specified current draw rating provides useful diagnostic information.

Disconnect the circuit from the voltage source before connecting the ammeter. The ammeter must be placed in series with the circuit being tested. Be sure that the ammeter's positive terminal is connected to the positive (battery) side of the circuit and its negative terminal to the negative (ground) side of the circuit.

NOTE: Never connect an ammeter across a circuit like a voltmeter. The ammeter could be damaged by the vehicle electrical system.

Excessive current draw is responsible for blowing fuses and, in some cases, draining the battery. An ammeter helps diagnose these conditions by locating the cause of the excessive current draw. On the other hand, there are times when a reduced current draw at a component (a power window motor for example) causes unsatisfactory performance of an electrical system.