Gauging interest / A Dedicated Headlamp Harness with Fuses and Relays / Concept / Demand ?

paul cain

paul cain

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When Galahad started the fuse panel project a year and a half ago, he asked about other electrical gremlins that haunt the E9 harness. I mentioned the BMW Electrical Engineering Department being asleep at the wheel when they designed the lighting circuit on the E9 i.e. -sending all the amps through the headlamp switch and then back and forth through the front harness. And then forgetting to put in dedicated fuses or relays. If you've experienced a front harness meltdown you know the effort required to recover full functionality. This a dangerous design. But it is fixable.

Is there interest in a new product that would be a stand-a-lone harness that would take its power source right of the + terminal of the battery and then distribute more than adequate current to the low and high beam circuits, including higher wattage H1 bulbs. This product would also incorporate both relays and fuses.

How big it is, where it sits, what it looks like and what it costs are TBD. Picture a hidden box the size of pack of cigarettes with two harness protruding, likely sitting in front of the radiator core support (behind the d/s headlamp). You can gauge the pricing competitiveness based on the fine fuse panel that is available today from Galahad.

This is just a kick off to discuss if the audience views this as a problem worth solving. Translation, a product that you would actually purchase.
 
paul cain said:
BMW Electrical Engineering Department being asleep at the wheel when they designed the lighting circuit on the E9 i.e. -sending all the amps through the headlamp switch and then back and forth through the front harness. And then forgetting to put in dedicated fuses or relays.
Click to expand...
Paul:

Well, it ain't quite that bad; there is a relay in the high beam circuit, but not one for the low beams. And, the high beam relay (and the adjacent horn relay) does get its power directly from the battery. While the low-beam doesn't have a relay, power to the low beam switch is fused. Although BMW didn't provide a low-beam relay, they did put a spare cut-out in the relay bracket, where a socket and relay for the low beam can be mounted.

But sure, the BMW Electrical Engineering Department's design is far from perfect. As I look at my wiring diagram, I see that the power feed to the relays is not fused . So while it is easy to add a low beam relay in that spare slot, that "fix" results in TWO unfused, high-current circuits (low beam & high beam), rather than one.

So yes, a well-designed harness/fuse/relay system would certainly be an improvement.
 
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Paul, i would be a buyer for the light harness for low and high beam with stand alone relays + fuses ... and if the relay is powered by the light switch to turn them on / off ... that would be great.
 
the other gremlin is the same approach for the electric windows - the downside is the pre-facelift cars vs the later cars ... as the harness needs are different. but the power feed from the battery to the motor with the switch powering the relays
 
rsporsche said:
the other gremlin is the same approach for the electric windows - the downside is the pre-facelift cars vs the later cars ... as the harness needs are different. but the power feed from the battery to the motor with the switch powering the relays
Click to expand...
There is another small company - this one is a one-man operation - making such a product for Alfa Romeo Montreals. See: https://www.alfabb.com/threads/power-windows.722476/#replies I know Gene Brown personally, and he's a straight-up guy. The connectors on his module are plug-in for the Montreal, but could be adapted to anything. It looks like the relays are double throw, so could handle either the sardine can, or E28 type of motor.

While the window application is similar to adding relays & fuses for headlights, bringing in a dedicated power feed to the doors is a bigger job than it is in the headlight area. Not that it's technically difficult; just more work to route a heavy gauge wire around the car into the door and rear seat areas.
 
Count me as another person interested. While I haven’t yet had any issues in my brief ownership, I’ve dealt with similar problems in other cars. I upgraded my fusebox this past weekend to the HolyGrailLabs box and it’s nice to know that while parts of the car are 1972, this portion is 2025
 
FYI - Paul is an expert engineer focused for decades on automotive applications.

Follow the leader….


I can’t imagine driving a coupe without a fuse and a relay in the low beam circuit.
Every car leaving the shop gets upgraded headlight wiring.
It’s easy, cheap and effective.

Besides keeping the rest of the wiring in the front loom safer- the addition of a relay right by the battery provides a huge boost in low beam light.

Voltage drop over distance is terrible for lighting..


Good reading from Daniel Stern:


Why Bother With Relays?

Power for the headlights is controlled by (wait for it) the headlight switch. In almost all vehicles built through the late '90s, and quite a few built after that timeframe, all headlamp current runs through the switch. That is: long lengths of thin wire to and from the switch, which contains tiny contacts. All of this adds up to a surprising amount of resistive voltage drop, which takes a big bite out of headlamp output.

In many cases, the thin factory wires are inadequate even for the standard original-equipment headlamps. There's a large element of automaker cost-cutting involved; it might sound like a joke to say they figure headlamps are only used at night, so that's a 50% usage duty, so they cut the wire gauge in half, but it's actually pretty close to how these kinds of decisions are often made in the auto industry where just about every last fraction of a cent that can be shaved from the build cost, will be.

And science has yet to give us the wiring, connections, and switch contacts that improve with age; in fact they do the opposite.

Headlamp bulb light output is severely compromised with decreased voltage. The drop in light output is not linear, it is exponential to the power 3.4. For example, let's consider a bulb with a rated output of 1000 lumens at 12.8 Volts and look what happens when it is operated at different voltages:

10.5V : 510 lumens
11.0V : 597 lumens
11.5V : 695 lumens
12.0V : 803 lumens
12.5V : 923 lumens
12.8V : 1000 lumens ←Rated output voltage
13.0V : 1054 lumens
13.5V : 1198 lumens
14.0V : 1356 lumens ←Rated life voltage
14.5V : 1528 lumens
(Outside North America bulb output and lifespan are both rated at 13.2v, but the effect of voltage drop is the same).

When operating voltage drops to 95 percent (12.54v), headlamp bulbs produce only 83 percent of their rated light output. When voltage drops to 90 percent (11.88v), bulb output is only 67 percent of what it should be. And when voltage drops to 85 percent (11.22v), bulb output is a paltry 53 percent of normal! It is quite common for factory headlamp circuits to produce this kind of voltage drop, especially once they're no longer brand new and the connections have accumulated some corrosion and dirt.
 
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sfdon said:
FYI - Paul is an expert engineer focused for decades on automotive applications.

Follow the leader….


I can’t imagine driving a coupe without a fuse and a relay in the low beam circuit.
Every car leaving the shop gets upgraded headlight wiring.
It’s easy, cheap and effective.

Besides keeping the rest of the wiring in the front loom safer- the addition of a relay right by the battery provides a huge boost in low beam light.

Voltage drop over distance is terrible for lighting..


Good reading from Daniel Stern:
Click to expand...
The Home Alone Stern?
 
I’d be interested in an upgraded headlight harness for my e9.

A couple of years ago a 2002faq.com member found Toyota was selling a complete kit to upgrade the 7” 1970’s Land Cruiser headlights to Koito H4s that worked on 2002s. Pre 1976 2002s had same headlights wiring issues lacking relays. The kit included two H4s, relays, fuses, wiring and zip ties. Available from Toyota for around $20. Yes $20.00
In installed one on my 2002 and it was completely plug and play, just had to mount relays. Obviously e9 setup is different. But devising a harness that installs as easily would be great.

“Install was easy, Plug the new leads into your headlights, plug the drivers side harness plug into the existing socket of your driver existing headlight socket, run the passenger side plug from harness behind the radiator and plug it into the bulb. The passenger side existing harness plug becomes obsolete. Attach the red wire to the hot + side of the battery, attach the black side to the negative side of the battery. Mount the relays and fuses wherever you like.”

Here’s the thread: (it’s a long one),
 
Dan Wood said:
I also would be interested or atleast the schematic.
Click to expand...
Dan, there is a schematic in the FAQ - post #9 in this thread
rsporsche

Thread 'E9 Parts dimensions, drawings, technical info and models'

Okay everyone, this thread is the new place to post drawing information, parts dimensions, data, etc. Any of the drawings on this post are only to be used for individual usage and not to be used for commercial profit unless approved to by the individual who created them.
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For me it comes down to pricing; this isn't complex to make yourself after all it's 'just' wires, connectors and fuses running differently (compared to OEM layout). Having something that is engineered well, though out, and available off-the-shelf is nice.

Once ready, my coupe will have some solution for this exact dilemma. I'm planning to do a lot of driving, say a 100 days/year, also in the dark, so solid power to the headlights is important to me.

The fear factor also helps the pricing....
not sure what the reason was, but this is my worst nightmare:
1759395593251.png
 
sfdon said:
FYI - Paul is an expert engineer focused for decades on automotive applications.

Follow the leader….


I can’t imagine driving a coupe without a fuse and a relay in the low beam circuit.
Every car leaving the shop gets upgraded headlight wiring.
It’s easy, cheap and effective.

Besides keeping the rest of the wiring in the front loom safer- the addition of a relay right by the battery provides a huge boost in low beam light.

Voltage drop over distance is terrible for lighting..


Good reading from Daniel Stern:


Why Bother With Relays?

Power for the headlights is controlled by (wait for it) the headlight switch. In almost all vehicles built through the late '90s, and quite a few built after that timeframe, all headlamp current runs through the switch. That is: long lengths of thin wire to and from the switch, which contains tiny contacts. All of this adds up to a surprising amount of resistive voltage drop, which takes a big bite out of headlamp output.

In many cases, the thin factory wires are inadequate even for the standard original-equipment headlamps. There's a large element of automaker cost-cutting involved; it might sound like a joke to say they figure headlamps are only used at night, so that's a 50% usage duty, so they cut the wire gauge in half, but it's actually pretty close to how these kinds of decisions are often made in the auto industry where just about every last fraction of a cent that can be shaved from the build cost, will be.

And science has yet to give us the wiring, connections, and switch contacts that improve with age; in fact they do the opposite.

Headlamp bulb light output is severely compromised with decreased voltage. The drop in light output is not linear, it is exponential to the power 3.4. For example, let's consider a bulb with a rated output of 1000 lumens at 12.8 Volts and look what happens when it is operated at different voltages:

10.5V : 510 lumens
11.0V : 597 lumens
11.5V : 695 lumens
12.0V : 803 lumens
12.5V : 923 lumens
12.8V : 1000 lumens ←Rated output voltage
13.0V : 1054 lumens
13.5V : 1198 lumens
14.0V : 1356 lumens ←Rated life voltage
14.5V : 1528 lumens
(Outside North America bulb output and lifespan are both rated at 13.2v, but the effect of voltage drop is the same).

When operating voltage drops to 95 percent (12.54v), headlamp bulbs produce only 83 percent of their rated light output. When voltage drops to 90 percent (11.88v), bulb output is only 67 percent of what it should be. And when voltage drops to 85 percent (11.22v), bulb output is a paltry 53 percent of normal! It is quite common for factory headlamp circuits to produce this kind of voltage drop, especially once they're no longer brand new and the connections have accumulated some corrosion and dirt.
Click to expand...
Hi SfDon,

Could you please share a bit more about this upgrade? Since I already have the harness out and I’m replacing some terminals, wires, and re-wrapping everything, I thought this might be a good opportunity to add these elements and make sure they’re as neatly presented as possible.

If you don’t mind, I’d really appreciate any details you could share about wire gauge, terminals, sockets, and placement. And I’m sorry for trying to squeeze all this knowledge out of you — I truly appreciate the ocean of information you’ve been sharing with us!
 
Someday when I get home and have time.......I'm in Porto now- last week with my daughter. Returning to states later this month and then leaving again.


I have to say that Paul is obviously more qualified to give technical advice- he is an engineer and I'm just an old wrench. Everything he does is better thought out and professional. Rather than just making it up on the fly- Paul is leading you down a road where you have instructions and everything is pre-cut and the right color and size and all the details have been thought out.
 
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This design oversight is rather astonishing to me... as the high current problem has been known for more than a century...


Everyone has heard the formula: P = V * I = I^2 * R ... power is voltage times current or current squared times resistance.

Shortly after Thomas Edison invented the electric light bulb, he teamed up with Westinghouse to build out a set of DC-powered electric street lights (it was a PR stunt). The PR stunt went quite well, and the general public was blown away seeing electric lights replacing gas lamps for the first time.

But a clever mathematician named Charles Steinmetz knew the team was headed towards disaster. Steinmetz understood the ohmic loss problem the nascent power industry would be facing... and thus argued for the superiority of AC power over DC power.

That is why long-haul power distribution is done at the 600KV or 1MV level ... P = V * I... if V is very large, I can be very small.. yet the equivalent amount of power is transferred via transformers and transmission lines. AC power enables the use of transformers.. P = V1 * I1 = V2 * I2


Obviously, we don't have AC power distribution inside a car, hence the use of relays for high power circuits. Relay control circuits require fairly minimal power and can be implemented with small gauge wire, reducing cable weight & cost. The relay contact side of the circuit - high power - requires large gauge wire to handle the current flow and can be in a localized area.. such as the headlight harness in this thread.

And in a strange twist, P = V * I keeps rearing it's head... as electrical demands in cars grew.. manufacturers were finally forced to switch from 6V to 12V systems.. My mom & dad owned a '67 Wolfsburg VW.. the year VW made the 6 to 12V transition.... And Tesla's cybertruck is the chief driver behind the latest transition..

P = V * I

or

P = 4*V * 1/4*I

Yes... if you jump from a 12V battery to a 48V battery, you can scale down the DC current by a factor of 1/4. And a 48V battery is low enough voltage you won't shock the piss out of individuals who accidentally short themselves across hot & ground leads. (Incidentally, 48V powered the old POTS telephone service before cell phones left landlines in the dustbin of history.)

In an electric car that has to deliver hundreds or thousands of peak amps to electric motors.. scaling down the current by 1/4 allows you to use significantly thinner copper wire.. and that leads to a significant reduction in cost and weight.


I wholeheartedly support this upgrade if properly constructed. Racecars utilize kill switches and relays for safety.. you don't want heavy gauge, high current electrical wiring criss-crossing the vehicle. In the event of a crash and severed wires... nobody wants a severed, high-current wire (400A for starter motors) near them. You want the entire electrical system shutdown. The E9 fire image posted by ErikNetherlands is very real. (Same for poorly wired Corvettes and fiberglass bodies.)


Apologies for the rant, but the electrical engineer in me couldn't resist.
 
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