Technical Challenge - power from Brake Light Circuit

[Mo Brighta]

Good morning all,

Here is a technical challenge for all - a good way to tap the brake light circuit.

This is a BRAINSTORMING activity, so ideas are not 'wrong' or 'bad' -- just think doable, simple, elegant, safe, reliable.
This is an OPEN challenge, meaning you may submit your ideas here in this thread, or privately to me.
I encourage discussion to foster ideas and adjustments to any and all proposals in the spirit of cooperation, NOT competition.
TWEAKING IS OK.

I want your ideas for sharing +12V power externally to the rear lights - for example, to feed a third brake light - on pre-1986 cars of the E30 persuasion. The idea is to install a simple harness with positive (or positive and negative) leads to power additional brake light(s) that are NOT part of the stock rear light, but are external, similar to the '86>' center brake light in the rear window (or trunk-mounted on Cabrios).

There will be two parts to this challenge, one for early (and most cabrio or 'vert) cars, one for late (facelift) E30 models.

The Rules- to meet this challenge, I will look for the following in your proposed solution:

>> must be effective, safe and reliable;

>> must be achievable by members with basic skills and hand tools;

>> involve minimal or no damage to the car wiring;

>> be possible without significant risk of damage to the lights;

>> You must be able to describe your method, and share with the forum;

I will be the sole and final judge in the evaluation of this challenge, and will remain open to your arguments and persuasion.

The period of this challenge is open ended, that is will continue until a reasonable and effective solution is derived and tested.
Criteria for the challenge (Rules) may change over time as opinions / ideas are received and development take place.
Testing of your proposals will be done in the Mo Brighta, Mo Betta Research and Development Laboratories in Golden, Colorado.

Put your thinking caps on, fellow gear-heads, and let's see if we can improve on what BMW came up with all those years ago.
If there is a real breakthrough in the results, I might even award someone with an unspecified gift of mutual consent.

Since you might be wondering, YES, this is to help provide a simple, effective power supply to the third brake coming in the Group Buy.
If I had your tail light here, specifically a 'cover' (bulb carrier) from one side of the car, I could install the subject power leads easily.
This is not a simple solution, because it requires downtime and shipping, and the associated cost and inconvenience.
Individuals with soldering skills can do this on their own, with minimal supervision and instructions.

I already have some ideas for early lights, but the late are more of a challenge, so let's see if we can collectively solve this!

Good luck to one and all, and may the best solution bubble up to the top!

Andy

[nando]

IIRC, most E30s come with an aux fuse panel that is meant specifically for adding additional 12v circuits. on my late car, it's located right next to the fuse box (although the clip that holds mine on has long since broken).

http://wedophones.com/BMWManualsLead.htm (I can't believe this link still works!) - find the ETM for the specific E30 you're looking for, and on the power distribution, look for the auxiliary fuse panel.

I just took a quick look, it is not present on 1984 and 85 cars, it starts in 86, and I'd bet all US cars after then have it. But it should be simple to retrofit, and I think the housing itself is still available new. As a factory design, I don't think it gets more functional or safe than this.

[Mo Brighta]

Thank you, nando. That link to the manuals is a vital resource for maintenance and troubleshooting of the wiring!

Your observation is a good one for adding electrical consumers that require independent fused power. Safe and convenient, and the FIRST suggestion received. Now let's extend this idea to providing power from the switched side of the brake light circuit. In other words, hot when you press the brake pedal. The idea is to 'slave' a third brake light (LED, low amps) to the existing brake lights, meaning it lights only when the stock brake lights operate.

The required current capacity will be 2-3 amps total draw, something I didn't mention in my original post... my bad. This means we will not necessarily need to add a relay to this circuit, not that there's anything wrong with relays... but that is an added complexity.

From the wiring diagram (1985 318 - 325e) there is power (violet/green wire) to the brake switch (pedal), then >> switched power<< (green/red wire) to the check relay DISPLAY (over the rear-view mirror) and the RELAY (over the left wheel well in the trunk), then to the left (green/yellow wire) and right (green/blue wire) rear lights. This is very similar to the circuit in my 535i, not at all surprising. This is probably true more or less for all the early threes.

You've already given me an idea ... THANKS!

Who else is going to chime in? Here's a hint - look at the connector to the check control RELAY in the trunk... not the display.

Andy

[NC325iC]

If I were going to wire in a third brake light to an early e30 that didn't have one I would do it at the driver's side (us) taillight.

Why?

• Running wiring into the trunk is easier than under the dash
• Shorter wire runs also
• The wiring harness runs along that side already so you'll be able to pass into the cabin easier if needed

How?

• The taillight connector is easily accessible and unclips easily from the taillight making the wiring easy to access
• The ugly way, splice into the ground and brake light wires with those little splice blocks
• The easy install way, make a connector extender that wires in your new leads and has matching mounting features to factory
• The elegant solution, remove the ground and brake light pins from the factory connector. Your harness has new pins to slide in their place. The new pins have 2 wires in each. Wire 1 goes to your brake light, wire 2 of each goes to a 2 pin connector into which the factory pins get connected.

What? No additional circuit protection?

• For an LED brake light? Nah you'll be ok

In newer e30s that have third lights already, just tap into those third lights in a similar fashion.

[Mo Brighta]

Well, someone has their thinking cap on!
This submission is loaded with calories, and not all of them are empty!

Well done, NC325iC, I have a question or two as I analyze your ideas. I'll contact you.

I am currently trying to track down E30s in my neighborhood to develop and test a prototype installation for early and/or late style lights. The 'Regional Groups - Colorado' topic seems to have near zero participation... Is there anyone in Denver or West Metro with an E30 out there? Owner willing to spend a little time and help the forum members out? I could make it worth your while with lighting upgrades / lamps / maybe a cold one... Contact me if you might be able and willing to help in this effort, and receive thanks from a Mad Scientist.

[downforce22]

Andy, as mentioned in the other thread I have an early model euro car (86 model year) which I was going to add an e28 3rd brake light to. It also means that this car has the rear fog light provisions being used with the rear fog light switch already so I can't do the dual bulb upgrade you pioneered. I also have two 91's models if you wanted to see them but am in colorado springs and dont make it to golden much.

I am not sure why you would need to modify late model cars that already have a 3rd brake light, but a thought on the early model cars after studying the e28 brake light is using the brake light check panel circuit on most late model cars (not present on the 318is). The e28 3rd tail light appears to already have a second pairing of wiring going to a circuit board build into the 3rd brake light housing (that is 4 wires going to the light fixture, 2 powering and grounding the lights, and 2 wires completing the check control panel circuit). So why not create an adapter between that PCB which powers the 3rd brake light check panel circuit? This would only work on early cars and assumes the pcb check panel circuit for the tail lights is wired the same as the e28 light, the pcb circuit is somewhere easily accessible, and that it is indeed a 12 volt circuit (not a smaller signal voltage). I assume the e30 has a similar setup but have not investigate what 'sets off' the check panel in the e30s or if you could just wire a light in series and call it good.

[Mo Brighta]

Andy, as mentioned in the other thread I have an early model euro car (86 model year) which I was going to add an e28 3rd brake light to. It also means that this car has the rear fog light provisions being used with the rear fog light switch already so I can't do the dual bulb upgrade you pioneered. I also have two 91's models if you wanted to see them but am in Colorado Springs and don't make it to Golden much.

OK then! Center brake light is possible.
Rear fog lights - who says you can't have both these and the upgrades? Dual filament is possible in both brake and rear fog, I have done it several times in E12 and E28 cars, E30 is also doable.
I will look for someone closer, thanks. If you are ever in town, just shout out.

I am not sure why you would need to modify late model cars that already have a 3rd brake light, but a thought on the early model cars after studying the e28 brake light is using the brake light check panel circuit on most late model cars (not present on the 318is). The e28 3rd tail light appears to already have a second pairing of wiring going to a circuit board build into the 3rd brake light housing (that is 4 wires going to the light fixture, 2 powering and grounding the lights, and 2 wires completing the check control panel circuit).

I never suggested there is a need for a third brake light in cars that already have one; someone said they wanted another, and that's OK.
I disassembled my 1986 E28 center brake to clean it up, found just what you said. Be glad to discuss wiring modifications for this with you - off line. But I suspect it will be overkill or overzealous. We'll chat.

So why not create an adapter between that PCB which powers the 3rd brake light check panel circuit? This would only work on early cars and assumes the pcb check panel circuit for the tail lights is wired the same as the e28 light, the pcb circuit is somewhere easily accessible, and that it is indeed a 12 volt circuit (not a smaller signal voltage). I assume the e30 has a similar setup but have not investigate what 'sets off' the check panel in the e30s or if you could just wire a light in series and call it good.

Hmm, I see what you mean - but look at the 2nd and 5th 'Rules' of the challenge. This may be a bit over most members' heads, and I'd hate to screw up anything in the brake light monitor, an important safety feature.
I think the LEDs are not 100% Perfect, but usually far more reliable than filament lamps. I would hope you will notice when it fails... which is probably never.

You do know that brake lights can be verified operational from the driver's seat, right? Reverse, tail, and turns can be verified by a walk-around.
You verify brake lights as follows:

>Back car into a space next to a plate glass window
>Look in rear view mirror at the reflection of the back of your car
>Test / verify all brake (and any other) lights off reflection in window - with key on, of course.
>Replace any failed lamps immediately from your spare bulbs kit (you have one of these, right?)

Again, thank you for your suggestions, This is all good food for thought.

Andy

[NC325iC]

https://www.ebay.com/itm/BMW-E30-Tail-Light-Brake-Connector-Pig-Tail-325-325i-325is-325ic-318i-318is-/184348091404?_trksid=p2349624.m46890.l49286

This is an example of the connector at the taillight in an early model. The thin rectangular section is the wiring connector, the wider section in the middle is a dovetail which slides into the taillight lens portion.

[Mo Brighta]

That is the same terminal inside the connector that I see in the Check Control relay box connectors to monitor tail, brake, and license plate lamps. Thanks - that is the information I was looking for.