Hi folks, I've just acquired a used fog light switch for use in a custom dash project mostly because it seems to match the other switches nicely. I'm hoping someone may be able to point me in the direction of a schematic for the switch that explains the various pinouts. This switch is from a 98-03 XJ8, is round with both rear and front fog light buttons on it. It has 9 pins.


Many thanks!

 

Here you go.....

 

Thanks a bunch Rob! I'll have a look over this and perhaps may have a question or two.

 

So, after pulling apart the switch and trying to trace out all the paths for the various pinouts on the mini circuit board in the switch I'm halfway to figuring out what seems to be a quite complicated switch. Of the 9 pins I have identified the purpose for 5.


The panel lights (not identified in the posted schematic) seem pretty straightforward and involve a -ve and +ve lead that seem to be isolated from all the other traces on the board. The 2 switches themselves seem to also be completely isolated and have an input each with a common ground. Push one and it grounds likely sending a signal back to a computer of sorts. Its the telltale LED's inside the switch that are giving me headaches.


The circuitry in the schematic seems to show a bunch of resistors and a PNP transistor related to each LED activation which seems like overkill to me. So, I'm thinking there's more going on here than simply lighting an LED when the switch is pressed.


My question would be about the operation of the fog lights themselves and if someone can shed some light (pun intended). For example, are the foglights "shut out" until the headlights are turned on? I'm assuming that the wiring all runs back to a computer of sorts that controls all this and that they aren't directly wired to relays, etc.


Any help would be greatly appreciated. Thanks!

 

Fogs come on with headlights or parking lights on: front fogs go off when high beams are on. Pin for each of those

 

Thanks Jim, I figured there was some form of "lockout" going on here. Still having trouble identifying the pins involved though. As I stated earlier, it seems that the panel light bulb is pretty simple. A +ve and a -ve pin unrelated to anything else that I can see on the mini board inside the switch. Also, the 3 pins involved for the momentary micro switches seem isolated from all other traces on the board. A signal trace to each switch which connects to a single ground common to both switches when depressed.


If this is true then there's a whole lot of circuitry involved just to turn the telltale LEDs on and off inside the switch. With 4 pins left unidentified you'd think that it'd be simple - a =ve and -ve pin for each LED. Obviously not.

 

Check out Fig. 10.2 also. The dimmer controlled functions appears to be for backlighting only, and that makes sense as the foglight LEDs are not controlled affected by the dimmer function.
Strangely, other LEDs like seat heaters are! I only mention this because the simplified drawing they give of the internals of components can be very misleading.

For the seat heater LEDs, the "dimmer override" goes to a transistor turn off the LED based on dimmer position.

 

Hi Rob and once again, thanks for the reply. I had noticed the pinout designated 10.2 on the schematic you provided but couldn't make sense of it. That's partly because of the wire colour shown which I interpreted as red/Light Green and the closest I could find that that was Red/Grey. Of course, upon closer inspection (and under better light) that wire could easily be Red/Light green. I retraced the path and discovered that the pin for that runs straight to the series of 3 transistors (of which only 2 are shown on the schematic - figures) on the mini board.


But, the fact that a pin runs to the start of the transistor might indicate that the switch's LED's act similarly to the ones on the seat heaters. That they turn off or dim depending on the dimmer's position. Can you tell me if this is the case with the fog light switch LED's?






Thanks!

 

I have two 308s and the foglight LEDs are not affected by the dimmer. Yes, the seat heaters and seat memory LEDs are. That's why I have some experience because I chased my seat LEDs all over the place before realizing the "dimmer override" line controls the LEDs.

Based on the wiring diagrams, the dimmer is supposedly only for the foglight switch back lighting. Never say never though I suppose.

All the other LEDs that have the dimmer wire going to them still work regardless of dimmer position on my cars.