Based on a look at the schematic for your headlights the most likely cause
of your woes is the dimmer switch. The low beam relay is also a suspect.
Less likely would be the 15 amp fuse for each low beam. The dash
integration module is the least likely culprit in my opinion.
The headlamps may be turned on in three different ways.
When the headlamp switch is placed in the ON position, for normal operation.
With the twilight delay switch placed in the ON position, for automatic lamp
With the twilight delay switch placed in the ON position, with the
windshield wipers ON in daylight conditions, after a 6 second delay.
During ALC control the headlamps will be in day time running lamp (DRL)
operation in daylight conditions or low beam operation in low light
conditions. The dash integration module (DIM) provides battery positive
voltage to the signal circuits of the headlamp switch. The signal circuits
include the headlamp switch headlamps on signal, the flash to pass switch
signal and the high beam input. With the headlamp switch in the ON position,
a ground path is available for the headlamp switch headlamps on signal
circuit of the DIM through the headlamp switch. The DIM provides ground to
either the headlamps high beam relay control circuit or the headlamps low
beam relay control circuit of the low beam circuit. The position of the
headlamp dimmer switch determines which relay control circuit has ground.
The DIM supplies battery positive voltage to the relay control circuits, if
the headlamps are necessary. The fuse block - underhood supplies battery
positive voltage to both relay switch circuits. When the low beam relay
control circuit is energized, current flow is to both low beam fuses and to
the low beam headlamps. The headlamps have ground at G103 and at G401. When
the headlamp high beam relay control circuit is energized, current flow is
to both high beam fuses and to the high beam headlamps. The high beam
circuit is divided into a left and right side circuit. The current flow of
the left high beam is from the fuse to the left high beam lamp. From the
lamp, the current flows to the normally-closed contact of the DRL relay to
G103. The current flow of the right high beam is from the fuse to the right
high beam lamp. From the lamp, the current flow is to ground at G401. When
the headlamp dimmer switch lever is pulled toward the driver, the
flash-to-pass switch closes. This grounds the DIM flash to pass switch
signal circuit. In response to this input, the DIM energizes the HDLP HI BM
relay. Both high beams remain on until the driver releases the switch
handle. If the low beam headlamps were on during a flash to pass operation,
the low beams remain on. The headlights may be switched to high beam with
the opposite movement of the headlamp dimmer switch lever.
Imagine that. Bad light bulbs. Reminds me of the time my wife told me that
the table lamp needed a new socket. I dutifully went to town and bought a
new socket. Replaced old socket with new. Turned on lamp. Still no light.
Bad bulb all along.
Two headlamps failing at the same time! Mighty odd. Have you checked the
output voltage from your alternator to make sure it isn't too high? Any
other bulb failures?
However unlikely, it is still possible that one went out earlier w/o
notice; and when 2nd one went, it'd be quite noticeable--esp. if one drives
very little at night. Hope that's the situation, in which case we'll
understand if you don't update us on such a determination. s
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