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Subject: Reason for rear fogs solo is... (LONG, usefulish for would be AE-ers)
Author: mrnobody : 137 posts
Posted on: 2008-09-17 11:21:52       		Bookmark and Share

...because I want to use them to power my AE and have 100% independent operation from the actual fogs, plus I'd like to see the little rear fog dash light indicator correspond with the AE being on. I have wired this completely and confirmed that the 4-way switch DOES NOT produced the desired behavior (actually, I confirmed it before I bought the 4-way).

Here's some detail about the LCM behavior for 99+. I installed the rear fog switch wire, put the rear fog outputs of the LCM to power the angel eyes, and then held all four wires that go to the Euro Fog switch in my hand to try various methods to get the rear to light WITHOUT the front. I even, for fun, switched the power outs on the LCM to power the front fogs via the rear power, and the AE as front, to see if some impedance problem was causing the fogs not to want to light separately. Not so. Rear with front only. Period.

Here's how it works. Rears are activated by TOGGLING ground while the fronts are on. You can connect rear to ground while the front are on, but they actually STAY ON even if you disconnect the rears from ground (however, NOT if you disconnect the fronts, either while rears are still grounded or AFTER disconnecting rears from ground -- fronts circuit broken = BOTH OFF). Anyway, on the rears, the next voltage change after ON causes them to go out. Openning the circuit (disconnecting) doesn't count as a "voltage change" but any other change that allows current to flow at a different voltage "toggles" the rears on/off/on/off.

I say any other voltage because you can toggle a hot wire instead of ground for the rears and they'll come on/off/on also, or hot, then ground, etc. Now...the LCM probably doesn't LIKE hot instead of ground, I'm sure it's supposed to be a ground circuit, but most of these things are protected against a low current draw/minor voltage surge so I took a few risks and messed with the LCM, but I'm sure the intended "toggle" is to ground (I lack a diagram for the 3-position 99+ switch...the Bentley diagram is for the pre99 4-position switch).

So, that's a long way of saying, the 4-way switch with the 3-way LCM will NOT produce the 4-way behavior. I simulated it in detail (and actually eventually bought the 4-way anyway and further confirmed). Also, the existence of and behavior of the 3-way switch reinforce that the behavior described (rear fogs ONLY w/ front) is by design.

The jadeturtle post (technically an e39 post) on rear fogs (the 2001 update, not on the BMWtips version of the post, but linked in on the jadeturtle website version of the post) describes the 3-way switch as being a toggle switch, and my conversation offline with Paul about it he suggested that the toggle implied spring loading that goes back to position 0 when the ignition is off, though he was speculating a bit and the update doesn't describe the behavior in detail. Based, however, on my testing, my assumption is the toggle is that the rear fog position toggles and springs back to position 1 "front on" from position 2, such that each subsequent toggle turns the rears on and off, while leaving the fronts on.

OK, back to the coding question. Now, there is a great post on e38.com about using the ground from the 4-position rear fog (bypassing the LCM entirely, ergo, essentially grounding two different things, the front fogs controller on the LCM and your AEs, independently via the same switch), and that's a good way to go. But, the Predator Orion wiring is different from the old DDE, so one can do this, but there are considerations (and with this post I will have essentially provided all of the info one needs to do what I did with the Orion wiring, but I'll still consolidate and organize for that sole purpose elsewhere later).

The Orion is driven by a relay with two triggers, merely connecting ground is not enough to light them, unless one of the triggers is also connected. So, one could put one of the triggers directly into the fuse box with a t-tap, which would give full ignition independent operation via the Euro Fog switch. One could put the trigger to the DTR, another common option, which gives full independent operation provided the key is to a position where the DTR are/would be (depending if you have them) on. I prefer this option because it keeps you from accidentally draining your battery leaving your AE on.

However, this leaves the secondary trigger, which one could put to the interior lights, for example, causing the AE to light when you unlock the car (and fade when you lock it). Of course, if the ground is NOT connected, the secondary trigger is useless, so if you use the independent operation wiring suggested before via the 4-position Euro fog, this secondary trigger will only work if you leave the AE in the on position (it's a mechanical switch, thus ground is connected whether the car is on or not) when you turn off the car (one more reason to wire the other trigger to the DTR instead of direct battery power).

Ultimately, that's what I did. I have independent AE operation via the fog switch when DTR would be on, AND I have the interior lighting synchronization as well IF I leave the fog switch in the correct position. If I forget, I don't get the interior light synch.

What I would LIKE TO HAVE is independent operation without having to leave my fog switch in any particular position for the interior light synchro to activate properly, AND the rear-fog indicator on the dash light to be synchronized with the AE being turned on. This is possible with the Orion in a pre99 car by wiring ground and AE power to the +/- ALWAYS (as intended with the product), and putting the two triggers to the interior lights and rear fog outputs on the LCM, wiring the 4-way switch as designed. Of course, maybe the current draw is insufficient on the LCM rear-fog out and would eventually explode your LCM (I doubt it, but who knows), but aside from that, this would be simple, nearly factory wiring with the best of all possible behaviors and with all the little glowy indicators that are so cool!

That said, there is another pretty cool alternative to what I did on these 99+ cars, assuming the ultimate option, involving LCM coding, is not available. That is, go ahead and wire the AE trigger to the rear fog power and live with the fact that they only operate with your front fogs on. If you are one of those who drives around with the front fogs on all the time, this may be OK with you. You get the correct operation of the interior light feature without regard for the fog switch position, and you get a that rear dash indicator light. So, trade-offs versus what I settled on.

Now, for real fun, you can switch the outputs so that the "front" powers the AE trigger and the "rear" powers the actual front fogs, meaning now you can have AE without fogs, but not fogs without AE (this involves taking apart the X12 and X38 connectors on the LCM --- TOTALLY PAINFUL, be warned). Either way, a person willing to live with this option might prefer the 3-position switch. 4-position might work (Jim Cash described the "rear only" as a "second off" position when he wired it this way), but the 3-position is actually aligned with the behavior of the LCM. Of course, 4-position means if we figure out how to code this you can improve the option to independent operation without buying another new switch.

One other cautionary note. When powering the front via the rear fog power, I found the voltage on the front DROPPED if one of the rear powered lights was out/disconnected. Strange. Makes me wonder if the whole thing is a bad idea, because if such a drop is caused by power running through the LCM somewhere that it should NOT be due to this odd wiring, well, that would seem BAD. However, given the LCM is software controlled mostly, I kind of doubt that's the case. Moreover, there's been plenty of discussion of running only ONE REAR FOG in an actual fog hook up, because that's actually the more typical wiring of rear fogs, which I would think would produce the same voltage drop (it's minor, but it exists), so unless people have had their LCMs fail after wiring one rear fog (I've seen no such post) then it's probably not an issue. Still, I spend a lot of time with this, so, full disclosure of MY RESULTS. As with any advice, best not to take it, or at least USE AT YOUR OWN RISK.

-Mr. Nobody


2001 740iL auto, Alpine White, Style 37 (daily), Style 4 (roadtrips), Orion v2 AE on Euro Fog switch, Quad Brake lights, DICE iPod Controller, 30K!
2003 530i manual, Jet Black, Style 19 (winter), Style 82 (3-seasons), Quad Brake lights, DICE iPod Controller, 45K

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