Fog light/trunk release switch not lit
Thread Starter
Le Mans Master
Joined: Jul 2011
Posts: 7,428
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From: Morristown New Jersey
Oldtimer
Fog light/trunk release switch not lit
hi folks, I have tried my best and for some reason My fog light/trunk release switch does not light up with the rest of the dashboard. The bulb is new, (in fact the original bulb did not work either)I've tried both sides for polarity. I cannot find a diagram that shows the pin connections, and I've also done the 9v battery "hunt and peck"method. Hoping for some ideas?
Last edited by chasboy; Feb 22, 2017 at 12:14 PM.
Safety Car
Joined: Dec 2010
Posts: 3,938
Likes: 498
From: Fords, NJ
That is not how I read the diagrams.
Power applied to pin 7 illuminates the background lighting for the switches in question. Power to pin 1 is the toggled supply to the BCM which tells the BCM to operate the fog light relay (39 in the engine compartment fuse box) which in turn provides the power via fuse 2 in the engine compartment fuse box to illuminate the fogs. The background lighting of the two switches is not dependent on the fog lights actually being on, only the parking or head lights being on.
Although the diagrams don't show it, pin 8 has to go back to a ground somewhere in the IPC. If it did not then the background lights for the fog and trunk switches could never illuminate. Power supplied on one side of a bulb (load) without a corresponding path to ground on the other side of the bulb (load) means an incomplete electrical path.
Power applied to pin 7 illuminates the background lighting for the switches in question. Power to pin 1 is the toggled supply to the BCM which tells the BCM to operate the fog light relay (39 in the engine compartment fuse box) which in turn provides the power via fuse 2 in the engine compartment fuse box to illuminate the fogs. The background lighting of the two switches is not dependent on the fog lights actually being on, only the parking or head lights being on.
Although the diagrams don't show it, pin 8 has to go back to a ground somewhere in the IPC. If it did not then the background lights for the fog and trunk switches could never illuminate. Power supplied on one side of a bulb (load) without a corresponding path to ground on the other side of the bulb (load) means an incomplete electrical path.
Thread Starter
Le Mans Master
Joined: Jul 2011
Posts: 7,428
Likes: 971
From: Morristown New Jersey
Oldtimer
That is not how I read the diagrams.
Power applied to pin 7 illuminates the background lighting for the switches in question. Power to pin 1 is the toggled supply to the BCM which tells the BCM to operate the fog light relay (39 in the engine compartment fuse box) which inturn provides the power via fuse 2 in the engine compartment fuse box to illuminate the fogs. The background lighting of the two switches is not dependent on the fog lights actually being on, only the parking or head lights being on.
Although the diagrams don't show it, pin 8 has to go back to a ground somewhere in the IPC. If it did not then the background lights for the fog and trunk switches could never illuminate. Power supplied on one side of a bulb (load) without a corresponding path to ground on the other side of the bulb (load) means an incomplete electrical path.
Power applied to pin 7 illuminates the background lighting for the switches in question. Power to pin 1 is the toggled supply to the BCM which tells the BCM to operate the fog light relay (39 in the engine compartment fuse box) which inturn provides the power via fuse 2 in the engine compartment fuse box to illuminate the fogs. The background lighting of the two switches is not dependent on the fog lights actually being on, only the parking or head lights being on.
Although the diagrams don't show it, pin 8 has to go back to a ground somewhere in the IPC. If it did not then the background lights for the fog and trunk switches could never illuminate. Power supplied on one side of a bulb (load) without a corresponding path to ground on the other side of the bulb (load) means an incomplete electrical path.
Thread Starter
Le Mans Master
Joined: Jul 2011
Posts: 7,428
Likes: 971
From: Morristown New Jersey
Oldtimer
Because in my amateurish method of electrical analysis, I figured there must be a ground pin and power pin, and the ohmmeter would be completing the circuit?
Anyway you're referring to pin 7 on the plug, not the the switch?
Anyway you're referring to pin 7 on the plug, not the the switch?
Melting Slicks
Joined: Mar 2001
Posts: 2,671
Likes: 850
From: New Jersey
Pin 7 of the Fog/Hatch switch illumination bulb gets +12V when the Park or Headlamps are ON. The other side of the illumination bulb is Pin 8, which gets PWM pulsed connections to ground, by the Instrument cluster. The duty-cycle of the PWM pulses is determined by the dimmer **** setting : for example, for half bright illumination, the pulses are 50%, for full illumination, they are 100%.
1) Verify you have +12V at pin 7 when the park or headlights are ON.
2) Connecting pin 8 of the Fog/Hatch switch to ground should cause the bulb to be full brightness (the Park or headlamps must be on).
3) If the bulb lights, then check (ohm continuity) the wire from switch pin8 to the Instrument cluster connector C1 pin B5. If that wire is OK, then the Instrument Cluster has an internal failure of the power transistor that functions as the PWM switch connected to C1 Pin B5.
1) Verify you have +12V at pin 7 when the park or headlights are ON.
2) Connecting pin 8 of the Fog/Hatch switch to ground should cause the bulb to be full brightness (the Park or headlamps must be on).
3) If the bulb lights, then check (ohm continuity) the wire from switch pin8 to the Instrument cluster connector C1 pin B5. If that wire is OK, then the Instrument Cluster has an internal failure of the power transistor that functions as the PWM switch connected to C1 Pin B5.
Last edited by ersatz928; Feb 24, 2017 at 11:07 AM.
Thread Starter
Le Mans Master
Joined: Jul 2011
Posts: 7,428
Likes: 971
From: Morristown New Jersey
Oldtimer
Thanks guys, after I read this about 12 more times and print it in large fonts, I will try everything you advise.! I'm also wondering if I'm misunderstanding when that bulb should be on. The DIC hud, and door switches light when I open the door. WHEN is this switch supposed to illuminate?
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Thread Starter
Le Mans Master
Joined: Jul 2011
Posts: 7,428
Likes: 971
From: Morristown New Jersey
Oldtimer