Pontiac Fiero 1988 Service Manual page 936

TROUBLESHOOTING PROCEDURES
Step
2 :
Read the Headlights electrical sche-
matic, see figure 9. This is the step that will
save you time and labor. Remember, it is
essential to understand how a circuit
should
work, before trying to figure out why it
doesn't.
After you understand how the circuit should
operate, read the schematic again, this time
keeping in mind what you have learned by
operating the circuit.
Since both low beams work, you know that
the Light Switch, the YEL wire, the Lo con-
tacts of the Headlight Dimmer Switch, termi-
nal IE of C100, the TAN wires, and grounds
G105 and G109 are all good.
Furthermore, since you saw that the High
Beam Indicator came on when the Headlight
Dimmer Switch was moved to Hi, you know
that the Hi contacts of the dimmer switch and
the LT GRN wire between the dimmer switch
and C100 are good.
At this point, you could test for voltage at
the RH Headlight with the dimmer switch in
Hi. However, it is extremely unlikely that the
high beam filaments have burned out in
both
headlights, or that
both
headlight connections
are bad. The cause must be a bad connection at
C100, or a break in the LT GRN wire between
C100 and the RH Headlight.
You have quickly narrowed the possible
causes down to one specific area, and have
done absolutely no work on the car itself.
Step
3:
Find the cause and repair it. Using the
Component Location List and the correspond-
ing figure, you can quickly find C100 and the
LT GRN wire, locate the exact trouble point,
and make the repair.
Step 4:
Check the repair by performing a sys-
tem check on the Headlights circuit. This, of
course, means making sure that both high
beams, both low beams, and the High Beam
Indicator are all working.
Now suppose that the symptoms were dif-
ferent. You may have operated the Headlights
and found that the low beams were working,
but neither the high beams nor the High Beam
Indicator were working. Looking at the sche-
matic, you might conclude the following.
It is unlikely that both high beam filaments
and the High Beam Indicator have all burned
out at once. The cause is probably the dimmer
switch or its connector.