Ohmmeter may be analog type (needle scale) or digital type (LCD or LED readout).
Both types of ohmmeter have a switch that allows the user to select different ranges of
resistance for accurate readings. The analog ohmmeter also has a set-adjust control
which is used to zero or calibrate the meter (digital ohmmeters do not require
calibration).
An ohmmeter is used by connecting its test leads to the terminals or leads of the
circuit or component to be tested. If an analog meter id used, is must be calibrated by
touching the teat leads together and turning the set-adjust knob until the meter needle
reads zero. When the leads are uncrossed, the needle reads zero. When the leads are
uncrossed, the needle should move to the other end of the scale indicating infinite
resistance.
During a continuity test, a reading of infinity indicates that there is an open in the
circuit or component. A reading of zero indicates continuity, that is, there is no
measurable resistance in the meter needle falls between these two ends of the scale,
this indicates the actual resistance, multiply the meter reading by the ohmmeter scale.
For example, a meter reading of 5 multiplied by the R×100 scale is 5000 ohms of
resistance.
CAUTION
Never connect an ohmmeter
to a circuit which has power
applied to it. Always
disconnect the battery
negative lead before using an
ohmmeter.
Jumper wire
A jumper wire is a simple way to bypass a potential problem and isolate it to a
particular point in a circuit. If a faulty circuit works properly with a jumper wire installed,
an open exists between the two jumper points in the circuit.
To troubleshoot with a jumper wire, fist use the wire to determine if the problem is
on the ground side or the load side of a device. Test the ground by connecting a
jumper between the lamp and a good ground. If the lamp does not come on with the
jumper installed. The lamp’s connection to ground is good so the problem is between
the lamp and the power source.
To isolate the problem. Connect the jumper between the battery and the lamp. If it
comes on. The problem is between these two points. Next. Connect the jumper
between the battery and the fuse side of the switch. If the lamp comes on. The switch
is good. By successively moving the jumper from one point to another. The problem
can be isolated to a particular place in the circuit
Pay attention to the following when using a jumper wire:
1. Make sure the jumper wore gauge (thickness) is the same as that used in the
circuit being tested. Smaller gauge wire will rapidly overheat and could melt
2. Install insulated boots over alligator clips. This prevents accidental grounding.
Sparks or possible shock when working in cramped quarters
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