Activating the Rear Fog lamp using (mostly) existing wiring

kent370

Activating the Rear Fog lamp on a USA-Spec 370Z using (mostly) existing wiring.

I've got a 2011 370z (USA spec). A few weeks ago, I installed a euro-spec rear fog lamp because I liked the look. I was planning on wiring it up to work with my brake lights, but when I installed it, I noticed a factory wiring connector right next to the non-functional USA-spec dummy rear fog unit. I plugged the fog light into it, but of course it didn't work. But it did make me wonder how much of the euro-spec rear fog wiring might already be in place.

I looked at the service manual as to how the rear fog was activated, and through some examining of the schematics, it shows that the rear fog light is activated by the *non-usa* MutliFunction switch on the steering column. Further wire tracing from this switch leads to the BCM (located in the passenger footwell). So as we already knew, the switch we need is not in our USA 370z's, but the wiring for the rear fog light *is* there (at least on my 2011 370Z).

But here's the good part: Using standard scotchlock tap connectors, I connected a momentary contact pushbutton switch on two of the wires from the BCM (145 and 87, to be exact) to simulate the function of the non-usa rear fog light switch. It worked! Pushing and releasing the button turns the fog light on, and pushing it again turns it off. And no additional wiring except for the switch itself.





Make sure you use a *momentary* contact switch only, and NOT a standard on/off toggle switch -- the connection only has to be made for a fraction of a second to be recognized by the BCM. The BCM reads the state of that circuit every 10 milliseconds or so to see if it is closed, and as soon as it sees a connection, it supplies power to the rear fog lamp. It keeps reading that circuit, and when it senses *another* connection, it cuts power to the rear fog. (Also note that the headlights must be on in order for the BCM to power up the rear fog)

The Bad News: Apparently the USA-spec guage cluster does NOT have the indicator for the rear fog light, so there is no way to tell if the fog light is on or off without getting out and looking at the back of the car. I'm still looking into this.

I'll post more when I find out more, but that's where I have come so far.

Cheers,
Kent

TreeSemdyZee

Nice. You ought to post a DIY with switch part, pics of wiring, etc.
I was curious about this when I wired up my Z store cable.

I turn on my rear-view camera to see if the fog is on/working

FLORIDA370Z

i wired my euro fog light by tapping into the license plate light..i spliced right into the pos and neg wires right where the go into the license plate light...its right behind the rear plastic in the hatch....so it turns on and off the the driving and head lights...took like 20 min.......love that fog light look..

kent370

I may eventually end up doing the same thing (hooking it up to the tail lights), but this is the kind of little project that piques my (inner geek) interest, so I rather enjoyed chasing it down and figuring it out.

Cheers,
Kent

FLORIDA370Z

i was doing the same thing with that plug before i chose to go with the easy route....

SPOHN

I've noticed this harness when installing my exhaust. Just assumed it didn't work due to the harnesses that come with the aftermarket fog lights.

Nice find. Can't wait for more info.

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spearfish25

Congratulations. You just reinvented the wheel. I did this and posted the DIY months ago.

DIY: Rear Fog Light Wire Via BCM and Stock Wiring

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2013 Cadillac V-Wagon, RIP Z

kent370

Sorry, I read through pages of the DIY section and didn't see your post, which is *much* more detailed and informative that mine -- good job. Thanks for letting me know.

Sorry to waste everyone's bandwidth; I'll try to delete this thread. If not, mods, please delete.

spearfish25

It's not a problem...I wish someone would have done it before I did. Took me a bit of time to figure it all out. And then there was the pucker factor of not wanting to mess up my wiring harnesses.

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2013 Cadillac V-Wagon, RIP Z

SPOHN

You the man

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