Chapter Nine
Electrical System
All engines covered in this manual are equipped with a
12-volt, negative-ground electrical system. Many electri-
cal problems can be traced to a simple cause such as a
blown fuse, a loose or corroded connection, a loose alter-
nator drive belt or a frayed wire. While these are easily
corrected problems that may not appear to be important,
they can quickly lead to serious difficulty if allowed to go
uncorrected.
Complete overhaul
of
electrical components, such as
the alternator or starter motor, may not be practical or eco-
nomical. In some cases, the necessary bushings, bearings
or other worn parts are not available for individual re-
placement.
If
tests indicate a unit with problems other than those
discussed in this chapter, replace it with a new or rebuilt
marine unit. Make certain, however, that the new or re-
built part is an exact replacement for the defective one re-
moved. Also be sure to isolate and correct the cause
of
the
failure before installing a replacement. For example, an
uncorrected short in an alternator circuit will most likely
bum out a new alternator as quickly as it damaged the old
one.
If
in doubt, always consult an expert.
This chapter provides service procedures for the bat-
tery, charging system, starting system and switches.
Wiring diagrams are included at the end ofthis book.
Ta-
ble 1 and Table 2 are located at the end
of
this chapter.
NOTE
Except where specified, F
and
D series en-
gines are includedwhen a basic model num-
ber is specified.
For
example,
if
model
3GM
is called out in a procedure, the procedure
also applies to
3GMD
and
3GMF.
BATTERY
Because batteries used in marine applications endure
far more rigorous treatment and are often used differently
than those used in an automotive charging system, they
are constructed differently. However, battery advance-
ments developed for automotive batteries have been ap-
plied to marine batteries. This has resulted in new battery
designs that provide the boater with more choices. A bat-
tery may be selected that better accommodates the electri-
cal requirements for the engine and the boat's accessories
than the typical older, wet-cell battery designs.
If
buying a new battery, consult with a marine dealer-
ship that sells a full line
of
marine batteries. To obtain the
best advice, provide the engine model and a list
of
electri-
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