Medium Duty Operator's Manual - Peterbilt Motors Company

Electrical System
Electrical and Alternator Precautions
Take the following precautions to avoid burning out
alternator diodes:
• Do not start the engine with alternator disconnected
(connections removed) from the circuit.
• Before welding, disconnect all electronic connections to
the vehicle batteries.
• Remove battery power cable and insulate it from the
vehicle. See “Welding” on page 249 for more information.
• Do not run the engine with the batteries disconnected.
Preventive Maintenance
• Do not disconnect the battery cables or alternator connection
cables with the engine running.
• Never turn the ignition switch to the IGN & START position
with the engine running.
• When charging the battery (installed in the vehicle) disconnect
the battery cables.
• Do not reverse the cables of the alternator, starter motor,
or battery.
• Do not polarize the alternator. The alternator should not
be polarized like a generator. To ensure correct polarity,
use a test lamp or a voltmeter.
– 222 – Y53-6008A Medium Duty (R05/09)