Circuit Maintenance And Repair - GMC G Service Manual

OHMMETER (Figure 7)
The ohmmeter is an instrument designed to indicate
resistance in ohms. It is used to test the condition of a unit
disconnected from the circuit.
Ohmmeter Calibration
When the ohmmeter probes are connected together, a
circuit is completed causing the meter needle to deflect.
The needle should read ZERO ohms, if it does not, rotate
the CAL or ADJ knob to ZERO the needle.
When the probes are held apart, the needle moves to
the maximum (infinite) resistance side of the scale.
The meter is now ready for use.
Figure 7 — Ohmmeter Circuit
VOLTMETER (Figure 8)
The voltmeter (properly observed) will give the techni­
cian more information than the ammeter, ohmmeter and
test lamp combined. Its application for troubleshooting here
is to measure the electrical pressure (voltage) drop in a
resistance circuit.
CAB ELECTRICAL 8A-5
To use a voltmeter for troubleshooting an electrical prob­
lem, connect it in parallel with the existing circuit. If the
voltmeter is connected in series with the circuit being
tested, the nature of the circuit would be changed and the
reading would have no particular value or use. Connect the
meter terminals according to polarity as shown.
The dash mounted voltmeter (in the vehicle) should also
be observed for monitoring proper operation of the gener­
ator battery cranking motor, and cranking circuit. In this
application, battery voltage drop can be monitored while the
engine is cranking; and after the engine is running, gener­
ator output voltage can be monitored. This can be a valu­
able first step prior to diagnosing other electrical problems.
CIRCUIT MAINTENANCE
AND REPAIR
MAINTENANCE AND REPAIR
All electrical connections must be kept clean and tight.
Loose or corroded connections may cause a discharged
battery, difficult starting, dim lamps, and possible damage
to the generator and regulator. Wires must be replaced if
insulation becomes burned, cracked, or deteriorated.
To splice a wire or repair one that is frayed or broken,
always use rosin flux solder to bond the splice and insulat­
ing tape to cover all splices or bare wires.
When replacing wire, it is important that the correct size
wire be used as shown on applicable wiring diagrams or
parts book. Each harness or wire must be held securely in
place to prevent chafing or damage to the insulation due to
vibration.
Never replace a wire with one of a smaller size or
replace a fusible link with a wire of a larger size.
WIRING CONNECTOR TERMINAL REPLACEMENT
(BLADE TYPE)
h 4! Remove or Disconnect (Figure 9 and 10)
1. Terminal lock tang (70).
2. Terminal (61).