Free ASE PREP – Reading Digital Multi Meter / BAR Diagnostic Course: Reading Digital Multi Meter:
Remember a voltmeter is connected in parallel to check for electrical pressure between two points in a circuit.
A Ohmmeter measures resistance it’s used to determine continuity and the amount of circuit resistance. Always disconnect the vehicle battery source before using an ohmmeter.
Ammeters are connected is series, and they measure current in amperes.
Reading-Digital-Mufti-Meter could be confusing, understanding the numbers and decimals are critical.
Ammeter are used in series:
Be-careful when reading an ammeter, a zero reading doesn’t indicate a perfect circuit it could indicate you have a blown fuse must cases you probably do. If you connect an amp meter to a circuit the circuit is drawing 15 amps an you have your meter set on the 10 amp scale the fuse will blow.
The rule of thumb for a normal parasitic current draw on a feedback computerize vehicle is 40 – 50ma.
Keep in mind the more computer’s on the vehicle the higher parasitic draw the vehicle may have, a modern day feedback computerize vehicle may have a 1-5ma draw and be perfectly normal.
Voltmeter’s are used in Parallel to check for electrical pressure
Remember when using an Ohmmeter you must remove power from the electrical circuit
Will a short blow a fuse:
Has you can see all shorts do not blow fuses, you may have a short across a circuit, for example you step on the brakes and the horn goes off.
That’s a shorted circuit and the fuse will not blow
If the hot side shorts to ground, the fuse will blow or if the circuit draws to much current over the allowable limit, then the fuse will blow