Author Topic: Rear Foglights and additional brake lights. (Read 32637 times)

ak96ss · « **on:** March 10, 2006, 09:46:35 AM »

For those of you who may be curious about how to use those two-button Euro switches that you see pop up for sale, or who want to add a rear foglight, I've written a brief description of the procedure I used.

I will be updating it near the end of the month with more details about the instrument cluster portion, where you swap out the existing indicator for one with the rear foglight symbol on it.

The file is hosted here, at http://m42club.com/writeups/lighting/rear_fogs_final_051109.pdf. It is a .pdf file, so you will need Acrobat Reader to view it.

Any questions, feel free to ask!

ak96ss · « **Reply #1 on:** March 13, 2006, 05:50:30 PM »

I'll reply to my own thread here...

I've confirmed that the PCB (printed circuit board) for the instrument cluster on my car supports the rear fog light indicator lamp. So, all you have to do is put a bulb in the right spot and apply power to the pin I circled in step 19 and your rear fog lamp indicator will function.

I'll rewrite the instructions at some point in the near future with the appropriate steps and, if I can find it, the part number for the electrical connector to use.

Febi Guibo · « **Reply #2 on:** March 13, 2006, 07:04:55 PM »

note: link to pdf fixed...

longtallsally · « **Reply #3 on:** June 22, 2010, 05:31:22 AM »

Can I revive this one?

So I had a question and have not verified yet in the wiring schematics I've got, but wanted to pose it to someone who has done this.

I'm currently in Germany with my US spec '91 318is and just nabbed a 2 button switch and the plug for it.

My question is if I can just jump power from the front fogs and run through that relay as opposed to adding a whole new one? I'm not planning on adding the brake light function as you mentioned (GREAT write up btw), so I won't need too much juice.

That said, as I can think of it, the only things I would need to do are:

- run a wire to the rear housing from the new plug and switch
- run a wire from the rear switch to the cluster for illumination
- tie the grounds together

Am I over simplifying?

longtallsally · « **Reply #4 on:** June 22, 2010, 05:53:35 AM »

Well, I've gone through the European manuals I've got and found this:

But the plot thickens from here. It says the relay that is next to the wiper relay is for the rear fog light in France and Switzerland, but that it also shares K4- the low beam relay. Interestingly, they have K5 as being the relay location for the power sunroof and windows, while that relay is generally vacant in US cars, unless you have heated seats (which I will very soon). Things that make you go hmmmmmm...

I still say I should be able to run on the US fog light relay (K8) as it is not a huge load to add, but am just trying to keep things clean. In all the modifications I've done, I am trying very hard to make sure I splice as little as possible.

DesktopDave · « **Reply #5 on:** June 22, 2010, 05:08:38 PM »

This thread is awesome. Keep it up...very inspirational. I wish we had them, they're great for safety...and why should only Volvo & Audi guys get to keep theirs?

longtallsally · « **Reply #6 on:** June 22, 2010, 05:34:19 PM »

I have to retract a bit of what I said; the K5 relay was in fact being used in my car, so I'm going to suppose (since the Bentley didn't confirm) that this is for the power windows and sunroof.

Of note, the K9 location has no wires at all running to it in the fuse block. Also, a number of the vacant fuses have a single terminal on them, but not the other?

I didn't take the meter to them to see whether the one was hot or ground, but it was interesting.

ak96ss · « **Reply #7 on:** July 31, 2010, 03:34:00 AM »

Sorry for the delayed reply - I never get emails when people reply to threads I've subscribed to...

Yes, in theory, you should have no issues at all just doing as you described. My only concern would be the extra load on the fuse for the fog lamps, but you'll find out soon enough if it's too much!

In regards to the vacant spots in the fuse block, some of them are constant +12V, some are keyed +12V - I've made use of a few other spots in the fuse block to make changes to the wiring and keep it stock looking. You just have to have the right connector to fit the backside of the fuse box, separate the halves, and fish the connector through to the correct spot.

It is a pain reassembling that fuse block when you are done, though.

longtallsally · « **Reply #8 on:** August 25, 2010, 08:51:48 AM »

OK, I'm moving forward with this now and still have questions.

I'm pretty sure I've decided to more or less follow your lead in terms of wiring. That is, I'm going to put in a separate relay for the rear fog and make use of the accessory fuse block in the engine bay.

My questions surround the switch wiring. I've done countless lights in my various cars and bikes, so I know how to do the relays, but for the life of me, I can't find the pin out of the OEM, US spec, foglight switch.

There are 4 pins on it, and 4 pins on the European switch?

?

So logic dictates that for the US spec switch:
- 1 pin to the headlight switch (so you don't turn the foglights on without any other lights)
- 1 pin to the foglight relay
- 1 pin to ground
- 1 pin to the cluster (for the indicator that they are on)

?

But which color is which? I've not taken the meter our and disassembled the dash yet to test myself, but wondered if you had some insight.

Could you also clarify which pin on the cluster plug should be given juice? I initially liked your idea of wiring straight to a bulb, but that spooks me with the possibility of frying the PCB if you put the bulb in backwards, and the pic in your write up is not particularly clear.

Finally, how did you test that? I'm assuming a simple continuity test to the "+" of the rear fog light bulb location?

ak96ss · « **Reply #9 on:** August 26, 2010, 05:35:38 AM »

What is that switch on the right? I've not seen that - mine looks like the left one.

Do both switches have two buttons on the front? They are really two switches in one housing - the two left tabs are one switch, the two right tabs are another. They are simply on-off, no other functions, so power goes in on one tab and goes to whatever device you are turning on or off on the other - basically fancy versions of a regular toggle switch.

So:
- 1 pin gets the gray wire for the front fog lights
- 1 pin get the gray/blue wire for the front fog lights

and then:
- 1 pin from your power source for the rear fog lights
- 1 pin to the rear fog light relay AND the cluster indicator

It doesn't matter which side you use for which function, they are interchangeable.

The US harness only has the leads for the front fog lights in it, the gray and gray/blue wires. The wiring for the dash indicator (front fogs) comes directly off of fuse 29 to the cluster. Take a look at page 6312-0 in the ETM. The way the harness runs, the front fog lights will only come on with your headlights.

The US harness does not have a corresponding wire in the harness for the rear fog lights, although the circuit board will support it. You'll have to add the wire if you want the indicator to light up.

With the cluster face down in front of you, the wire you want to add will connect to the right side cluster connector (C2, white), bottom-left pin. I don't have a harness in front of me to get the pin number off the connector, but it's pretty straight-forward.

Yes, I just did a continuity test from the pin on the back of the PCB to the front, where the hole for the bulb is. I also have my car wired this way now, works fine.

Clear as mud?

longtallsally · « **Reply #10 on:** August 26, 2010, 06:00:09 AM »

Sorry, should have clarified. The switch on the left is the "euro" one and the one on the right is a US Spec one:

So what you said makes sense for the european switch, but I still don't get the US spec switch wiring. I've not removed mine yet, but are there actually 4 wires hooked to it? I also don't know why there are 4 posts on the switch I've got pictured there- perhaps it is a different year? I just grabbed one while at a yard a long time ago and assumed that they all had 4 posts.

Ironically, JUST as you posted this response, I was finishing downloading the updated electrical manual you posted which gives me just what I needed, since the other one that was posted was missing those pages. I've desperately wanted many of the missing pages as I've been looking at the other one for other things and those missing pages were killing me.

The clarification on which post of the cluster connector is a big help- in your write up, it looks like it is the second one up on the right. But now that you mention it, I can see the circle around the bottom right post. I wanted to do a continuity test anyway, but thanks for the clarification.

I should be sorted now, save the US spec switch wiring/posts. THANKS!

EDIT: And now I see that the wiring diagram you posted is for US spec cars with the dial filament low beams and single circuit to the fog light switch. And the fog light switch does in fact go to the headlight switch for its power. So I bet you can have your headlights and parking lights off and still have your fog lights, can't you?

DesktopDave · « **Reply #11 on:** August 26, 2010, 06:56:54 AM »

You didn't need to clarify that picture. It does look a little like a power window switch though.

longtallsally · « **Reply #12 on:** August 27, 2010, 08:32:03 AM »

So now that I've studied the wiring diagram, I'm going to make a pretty minor change to the the design John did.

Instead of going through the hassle of fishing a wire through the firewall for the switch power, I'm instead going to pull it off the front (US spec) wire that goes to the headlight switch.

I'll still be using a secondary relay in the trunk just for the rear fog light.

My logic/reasoning for this is twofold:

1- This is just the power to the switch telling the relay in the trunk to turn on the light back there, so it is not bearing the full load of the light itself, and therefore shouldn't create any issues as it should only be a minor load.

2- This way, the rear fog light is tied not only to the ignition, but also to the headlight switch. This will prevent the rear fog light from being on without either the parking or headlights on.

Please tell me if my logic is off base on this.

My only concern is that I will be asking the dash indicator to come on in an "un-relayed" manner. If you study the diagram below, you will see that the dash indicator is on the same circuit as the left hand fog light and is only activated after the relay is activated by the switch.

It will work the way John described, but I think it will end up putting undue stress on the switch and the dash bulb as the dash bulb won't be "behind" the relay. So where this will be a PITA for me is that I now have to run a second wire from the relay in the trunk to the indicator bulb for the cluster. Grrrrrr...

ak96ss · « **Reply #13 on:** August 28, 2010, 06:07:27 AM »

Yep, I considered that, and ended up fishing the wire from the front. It wasn't that hard, and it's on it's own circuit that only gets power in RUN anyway.

I don't think you'd have a problem just running the 'un-relayed' configuration, as the dash bulb is only like 1.2w, but I'm with ya.... the added benefit is that you will see that bulb is actually getting power out of the relay, rather than the way mine is wired, which only shows that power is going to the relay and not necessarily out of it.

longtallsally · « **Reply #14 on:** September 03, 2010, 07:31:17 AM »

OK, I can't get it to work. I'm lost. I started a thread, but am going for multiple exposure here so if you could check this thread and offer some advice on what I could have done wrong that would be great:

http://www.m42club.com/forums/showthread.php?p=96185#post96185

EDIT: Nevermind, I figured it out. You canNOT use the headlight switch for power after all. I ended up wiring it in the exact same manner as John. I can't see another way...