I'm planning out a rear work light install on my D2. I live in San Diego, so the OEM rear fog lights aren't ever needed. My plan is to tie the work light into this circuit.

The problem: The existing wiring requires the headlights be on to power the circuit.

Does anyone know how to rewire the circuit to work with keyed or constant power?

********************* SOLUTION *********************

I can now control the rear fog circuit without having the headlights on.

(1) Rewired the Rear Fog light CONNECTOR to work with a Cruise Control switch
(2) Trimmed guide ridges the Rear Fog light CONNECTOR to fit into the Cruise Control switch (very easy with a box cutter).
(2) Moved the Fog Light switch PLATE to the Cruise Control switch (very easy. held on by light clips)
(3) Ordered a new Cruise Control switch from eBay, $24 shipped (to replace the switch I repurposed).

You can use either constant or switched power for the new power source. I went with constant, tapping into an existing run I had added for an additional USB power point. Yes, the amber 'on' indicator on the switch illuminates when the lights are on.

 

You'd need a different switch as well then. The fog switch is momentary so you'd have to stand there and hold it if you wanted the lights on.
Perhaps just get a non-momentary D2 switch for either the instrument nacelle (e.g. rear wiper) or the cluster area below the climate controls (hazard, hill descent) and use that. Keyed power is available from an unused terminal in the driver's side fuse box.

 

My plan is to use the existing circuit. I'll draw power from the existing rear fog lights. This won't require having to replace the existing switch.

I'm ONLY trying to get around having to have the headlights on to use the rear fog circuit.

 

That will be controlled by the BCU. I don't recall seeing an option to change it.
You don't need the headlights on though. Marker lights are enough.

 

I tested earlier, the FRONT fogs work with just the markers, but the REAR requires the headlights.

 

When I wired in extra bezel switch for light bar I recall sourcing a cruise control switch. The fog lights were “latching” or “trigger” switches best I recall. they will have different pin orientation then what your after. I did run my own 12v w relay tho.

imagine you could reuse the wire ran from the rear fog to dash bezel as it’s run interior to rear to save on some wiring..

pop the cover off the cruise switch and use the rear fog cover for aesthetic.

 

The fog switches aren't latching, they're momentary.

 

I understood a momentary switch is “on” only when depressed.

a latching/ trigger switch is available when another power source/switch is “on” - and will remain on when pressed once. Then pressed again for off & will remain off..

your not holding the fog light button to illuminate. You press once & they’re on until the trigger source is disconnected?

 

Exactly right. But the front and rear fogs are controlled by the BCU. All the switch does is send a trigger signal. That's why the lights are not still on when you turn the ignition off and then back on again.
D2 Electrical Library, page 4.121: "The rear fog guard lamps are controlled by a non-latching switch located on the left side of the instrument pack."

 

Gotcha.