Electrical System; Wiring Diagrams; Fusible Links; Circuit Breakers - Hummer H1 Service Manual

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DIAGNOSTICS
The following section of the service manual deals with electri-
cal diagnostics. The section consists of three main tools:
1. Diagnostic charts

2. Wiring diagrams

3. Connector legend
Diagnostic Charts
Diagnostic charts are designed to take you through individual
steps to locate a problem. The steps start at a point in the elec-
trical system and progress to find the problem without over-
looking items that may be contributing to the problem. In most
cases the chart will refer to a wiring diagram, and connector
callouts, both of which are provided for reference. The charts
are designed to find problems which are current, not intermit-
tent. These charts do not include preliminary visual checks.
The preliminary checks must be done prior to using the charts
for diagnosis. If the checks are not done, a simple problem
such as a blown fuse may be overlooked.
Wiring Diagrams
Wiring diagrams give a visual representation of the vehicle
wiring the diagnostic charts refer to. The wiring diagrams in
this section are broken down into systems. The diagrams will
include any part of the electrical system which pertains to the
system being diagnosed. Refer to the connector legend for con-
nector identification of system connectors.
Connector Legend
The connector legend is a reference library of all the vehicle con-
nectors that are called out in the wiring diagrams. Included are
drawings of both male and female connector halves called out
with pin/cavity arrangement, and a listing of all included circuits.

Preliminary Checks

The diagnostics in this section are designed to find problems
that are not obvious. Before starting any formal diagnostic
chart, preliminary checks must be performed. Preliminary
checks should include:
• Visual inspection of all components
• Inspection of any fuses related to the system
• Connector inspection
• Inspection of electrical harnesses
• Charging system and batteries
These types of checks are not included in the diagnostic chart.
In fact, most of the charts rely on the fact that you, the techni-
cian, has performed these initial inspections.
Diagnostic Strategy
Whenever a vehicle is being diagnosed for a problem, a strat-
egy should be used. The following charts are strategy based,
meaning they all follow the principle of starting simple and
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Electrical System

working step by step to more complex tests. This allows prob-
lems which may be small in nature to be found quickly, and not
overlooked. NEVER skip steps in a diagnostic chart. Each step
relies on a previous step for correct diagnosis. Avoid random
diagnostics and parts replacement which can lead to long, ex-
pensive diagnostic times and may not reveal the problem.
Intermittent Failures
ALL of the charts in this section are for use on current failures.
Do not attempt to use these charts to diagnose a problem unless
you are sure the problem currently exists. If the problem is in-
termittent, parts will be unnecessarily replaced, or no problem
will be found.
BASIC ELECTRICAL CIRCUITS
WARNING: When removing battery cables, disconnect
ground cable first. Ensure all switches are off before
disconnecting battery ground cable
General
An electrical circuit is a number of electrical devices which are
connected in a loop from a positive voltage source (battery
positive) to a negative ground source.
Parallel Circuits
The Hummer electrical system is a parallel circuit. In a parallel
circuit, the electrical devices form more than one current path
to and from the power supply. The supply voltage is the same
in each path.
Circuit Components
A normal circuit path starts at the power supply (battery system
or alternator). Next in line is the circuit protection: fusible link,
fuse, or circuit breaker. The circuit load, such as lights, motors,
or solenoids completes the circuit to the ground system.
Circuit protection devices

Fusible Links

A fusible link is a section of wire, usually two gauge sizes
smaller than the circuit it protects. If the current rating of a fus-
ible link is compromised, the fusible link will melt open.A spe-
cial insulation prevents wire fires, and swells when heated to
indicate the position of the open in the wire.

Circuit Breakers

Circuit breakers are electrical mechanical devices that will act
as a fuse to prevent excess current flow in a circuit. Unlike
fuses, the mechanical opening of contacts stops current flow.
The contacts will reset in a short period of time. This process
will repeat until the current excess is stopped.
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