Re-wiring brake and fog lights the other way around..

[M3wannabe]

Has anybody ever seen it done, or know how to do it??

I basically think that having the brake light on the inner-most globe of the tail lamp assembly looks a bit average..... and would like to reverse the fog and brake circuits...... so when I brake, the circuit will make the outer-most globe illuminate (similar to a '90s 7 series does).

I would basically prefer to have my rear fog lights in the location directly either side of the number plate.

I dunno..... every time I see E36's at night time, the narrow brake lights seem to annoy me. Modifying mine would make my car a bit different.... in a sneaky kinda way.

[AW328i]

Cool idea! Find the wires and switchem I guess?

[bimmer dot info]

I'm not to familiar with the e36 but i would think that you could switch the wiring in the harness.
Does the e36 have a CCM that will complain that the bulbs are out? Do they use the same type of blub? If the brakes are dual filament and the fog lights are single that will probably cause some problems. If the wiring is exposed like the ones on ebay and blubs match it should be very easy time switching them right there.

[johnf]

Both filaments are 21W and should appear the same to the check control module.

Personally, I would light both the rear brake lights and rear fog lights to really show I am braking. That would probably either annoy or neuter a CCM.

[M3wannabe]

Yep, both bulbs are 21/5W dual filament.

My E36 is a 1992 model..... CCM?? No idea.... but it doesnt have an OBC, which was my main concern.

The only issue/unknown I have is the wiring. I am not sure how the 2 assemblies are wired to each other.... eg: whether one assembly feeds the other assembly, or if they are independant.

I was HOPING that the conversion would be as simple as reversing 2 of the wires in both plugs.... but thought I should ask the wealth/lack of knowledge found on this forum first.

JohnF.... yes, I agree, that would be the BEST idea.... but it would probably involve removal of the rear fog option to accommodate it. I would assume that you would tap a relay off the brake circuit which would supply power the fog globes when the brakes are pressed..... and having the original fog light power supply completely removed or keep it connected but isolated using a diode..... not that hard really....

Hmmmmm... and considering that it doesnt snow in this part of Australia, I think that removing the fog option is the easiest answer to my problem. Thanks!!

[bimmer dot info]

If you want fog and brakes lights to come on with the brakes you could wire a relay in to the brake circuit that would send a signal through the wiring just after the fog light switch. Shouldnt cause any problems if you use a relay with enough resistance on the coil (you would need to find/run a wire to provide power through the relay... or you could use the power wire at the fog switch). Then you would get fog and brakes on brake application and you could also set the fog lights to always on with the switch.

If my description does not make sense i'll try to draw you a picture.

[M3wannabe]

Yep I understand.... I just thought that it would be easier to conceal the whole lot in the boot .... closer to the battery. The dash has enough crap under there already!!!

And if I was to remove the rear fog light option completely, it would give me the oppotunity to use the fog switch for some other stealth application..... :thumbup: ;)

Good idea though.

[bimmer dot info]

Try one relay one each side attaching the brake lights to the fog lights. Run another wire if you are worried about running 42W through the factory wiring (I dont know what gauge it is). That should get you what you want and then you can just disconnect your fog light switch (the car shouldnt realise that it is gone) and use it for your stealth application.
Only problem would be if the CCM bitches about the extra draw from the relays coil in the brake circuit.

[M3wannabe]

CCM? Please explain.

Central Control Module???

I have no computer inside the car on the dashboard, just the ECU which is accessable via the engine bay..... There is nothing that would tell me "Brake Light Failure" or anything like that on my car.

[bimmer dot info]

CCM is a check control module. Detects burned out bulbs and such. I was not sure if your car had it. It does not look like it does. Makes this easier for you.


After hearing you talk about this I've been thinking about doing the same to my car. (my car is US spec and does not have rear fog lights installed). Thanks for the idea.

[johnf]

You could nearly swap the rear fog lights with the brake lights by popping out and swapping the corresponding contacts in the plugs to the rear lamp assemblies -- except that BMW daisy chains the left brake light on a LHD, non-check control car to the right brake light and then runs the right brake light to the brake light switch. (You should be able to swap the contacts on a check control car.)

Using a relay to double up the rear brake lights is a good idea even if the car does not have check control. The E36 brake light switch is already overworked driving the normal 3 x 21W = 63W of brake light bulbs, as countless people can attest who have had to change the switch. Adding two more 21W filaments for 105W of brake lights will probably lead it to an even earlier demise.

I 100% agree about wanting to put relays and such in the rear of the car rather than under the cramped dash. Below is a little controller I designed and built to make the brake light switch last the life of the car and to monitor the brake lights. I found plenty of room near the right brake light (where the controller could interrupt the daisy chain), got down to sheet metal with just my bare hands and simply attached the controller to the trunk wall with velcro. (BLCC = Brake Light Check Control)

[M3wannabe]

Yep, did my research last night....

Its easier to do the fog/brake position swap on a car equipped with a CCM. Its just a matter of swapping 2 of the pins in each plug.

Doing it to a non-CCM car is harder due to the daisy-chaining you mentioned (but still easy enough)... its just a matter of pulling 3 wires out of one of the plugs, joining two of them together, fitting 2 pins back in to the plug and leaving 1 pin disconnected.

The annoying thing I found is that the wiring changes between E36 body types AND year models, so it is impossible to write up a simple "this is how its done".


Also, after doing a fair bit of thinking, Ive come up with a 3-relay setup which will allow the fog globes to be used as brake lights OR fog lights, depending on whether the fog light switch is on or off. Its a bit more work, but a lot more "cool".

And then I started thinking a bit more, and came up with a design for a Police style flip-flop between the brake and fog lights. Thats when I decided to stop thinking.... not a ricer any more, cant have that stuff on my car.....

[johnf]

I was not aware that BMW changed the tail light wiring from one year to the next. If you happen to have an example where a model with check control or a model without check control changed from one year to the next, I can check a tolerable few ETMs and see if it's a drafting errors.

A single DPST (black) relay should suffice to drive the rear fog lights from either their switch or the brake switch without lighting the rear fog light pictogram when you brake:

the NC conact to the rear fog light switch
the N0 contact to term R (hot in acc/run/start)
the commuter contact to the rear fog lights
the coil to the brake lights.

Happy modding!

[M3wannabe]

Just wondering if I see a problem with wiring the relay that way...... the brake circuit power supply is coming from the brake light switch, and will therefore load the switch up to 105W, as you mentioned not to do??

Sorry if im being picky..... its just that other people might try this mod....

[M3wannabe]

If you happen to have an example where a model with check control or a model without check control changed from one year to the next, I can check a tolerable few ETMs and see if it's a drafting errors.!

Ah, nope... sorry, I misread the page reference for the 1992-93 and 1994 onwards 318i...... hey, it was late at night!!! :angel:

Body shapes definitely have different wiring....


Question.... LHD and RHD cars.... are the plugs in the same locations, or is everything back-to-front?? I would expect the loom under the dashboard to be very different (in length) if the loom isnt reversed.

[bimmer dot info]

Wire the relay or relays with the coil attached to the brake light circuit and a ground and the variable contact in the fog light circuit. Find a power wire (always on. if you have a sub that wire will work great) back there that you can hook up to the high power input on the relay. The fog switch and fogs with brakes features will work and the light shouldnt show on the dash when just using the brakes.

[johnf]

I, personally, would supply the switched power I suggested to the normally open contact. If you supply unswitched power and the contacts weld shut (from switching cold rear fog light filaments) the lights will flatten the battery within a day.

I don't remember seeing any pin changes between LHD and RHD cars, but perhaps I haven't looked beyond the many changes needed for Sweden and Norway. (Once again, I have been distracted by the Swedish model.)

[M3wannabe]

Took a few photos of the modification...

http://img.photobucket.com/albums/v716/sc850/BMW%20Personal/06-11-11a.jpg
^^^This is the normal brake light setup.

http://img.photobucket.com/albums/v716/sc850/BMW%20Personal/06-11-11d.jpg
^^^This is the inverted / customised brake light setup.

http://img.photobucket.com/albums/v716/sc850/BMW%20Personal/06-11-11c.jpg
^^^This is stage 2 of the brake light modification, with all 5x 21W globes being used.


This modification was only done temporarily so I could sort out and plan all the relay and wiring changes. Not sure if I like the 5 globe setup or not. :confused: