SWB Relays Analyzed

[304065]

Here is my modern workaround for the NLA Stribel flasher can, 901 615 341 10. The can is connected as in the diagram above, when you pull the hazard switch it completes the ground to the "S" terminal. It also grounds 85 in the control light relay, which energizes the control light relay and removes the blinker relay from the circuit.

Porsche did that for two reasons: first, not all cars came with the hazard circuit. Certain Euro cars didn't have it. There are instructions in the FWM for retrofitting the hazards to cars that didn't originally come with it-- that's where the diagram above comes from, actually. Second, you shouldn't have the turn signals going at the same time as the hazard.

Now to the diagram. This workaround (the "Kludge" in honor of our four-cylinder friends) is constructed from two el-cheapo "Bosch Style" ice-cube relays and a generic EL13 flasher unit. These should all be available anywhere, you could probably find them in a gas station on Easter Sunday were you so inclined.

The Kluge's logic: you need to put a load on the flasher to get it to heat up and blink, so rather than using the flasher output to power the 86 relay coil input of a pair of relays, you put one side of the car's signal bulbs and wiring in series with the flasher to load it, then drive the other side's 86 relay coil in parallel. It looks harder than it actually is.

Analyzing the circuit step by step: first the grounds. You've got ground wires connected to both relays 85 terminal, that's the ground. Both grounds are connected to the wire that previously went to the "S" terminal, a white/red wire. It's this wire that goes through the factory harness to the hazard switch and when the switch is pulled, to ground.

Next: the green/white "30" or direct battery connection wire from the can goes to the 30 inputs on both relays, and also to terminal 86 on one of the relays. Pretty simple. When you pull the switch, this current finds its way to ground through the relay coil (energizing it) and out through the 85 terminal and the circuit I just talked about above.

When that relay is energized, current flows from the 30 to the 87, normally open input. Connected to the 87 terminal is one terminal of the flasher. In this case, X stands for power. Connected to the "L" terminal is the load, in this case, the blue/yellow +black/white "L" wire to the can (which is just a coincidence, I did that to make it easier to understand, not harder) which stands for Left Side bulbs. Also connected to the "L" terminal is pin 86 from the OTHER relay, which, when the flasher is putting out current to the "L" terminal, energizes the relay's coil and completes the circuit, allowing power to flow from 30 to the black/green "R" wire, or the RIGHT side of the car. (The "P" terminal of the flasher is not used, that is the "pilot light.")

Simple, right? Pull the switch, ground relay #1, current flows to the flasher which is COLD, so current flows to the LEFT bulbs and to ground, lighting them, and to the other relay's coil and to ground, which turns on the RIGHT bulbs. It all happens so fast you can't see it. The flasher heats up and breaks the circuit and the LEFT bulbs go out and the relay coil de-energizes and the RIGHT bulbs go out.

The other photos show how easy it is to wire, and what it looks like next to the old can. It's all hidden behind the driver's footboard, impossible to see.

[Allen Henderson]

Raj!

If the hood lights (100 watt bulbs per light) are on a separate switch for the pair and it is one of those heavy duty, 25 ampere switches, a relay shouldn't be necessary.
Again, the 25 amp switch can handle 300 watts of 12 volt power (12 x 25 = 300)

-Allen-

[Allen Henderson]

Allen

That was easy.Why did you use the gray relay on yours as opposed to the yellow(i am assuming it has nothing to do with wattage)and for the cibie biode headlights what should i use?Also,the original gray relay for the headlight for your car would not that have worked for your 100watt headlights

Raj

Raj,

The yellow relay is "normally closed" and when power is applied to the input side of the selenoid it opens. You need the opposite for turn on lights rather than turning them off (remember the yellow relay turns off your fogs when the high beams come on). MAYBE the original gray relay, switchover relay, would have worked without the round LWB I added but those are old relays and I don't know their current rating; so I have a "belt and suspenders" for my H1s.

For the cibie headlights (what is their wattage?) you can probably do nothing or add a "belt and supenders" grey or round relay.

-Allen-

[MarkS]

John thank you for taking the time, this is VERY good info . I make a motion it goes into best of tech. Mark

[Rich Lambert]

John, thanks for putting together something I can actually read without a loupe.

I wish I'd had this before I spent hours troubleshooting my flasher circuit.

[304065]

Some wire sizes from the SC diagram.

D+/61 Blue to pin 11, 1.5mm^2
DF black 1.5 regulator to alternator
B+ red to starter, 10mm (that's a big fat one)
B+ red to pin 14, 2.5
Tach pulse lead (TD on the six-pin box) black/purple 1.0
Yellow from ignition switch to starter- 2.5
Red/black from ignition switch to engine compartment- 2.5

[304065]

Hmm, some more work on wire sizes.

The voltage regulator wires are all 1.5mm^2 according to the factory. That puts it squarely between 16 and 14 gauge. I measured the OD, they are 2.6mm, but that includes the insulation. Wire gauges are expressed in terms of the diameter of the WIRE, without the insulation. Also, an AWG measurement is for a solid wire, so a stranded wire of the same AWG will be larger in diameter due to the spaces between the strands. I will probably use 14 gauge.

The white/yellow wires from the fog lamp switch measure 2.8mm OD. That matches 14 gauge pretty closely.

The horn relay wires are bigger, the ground is 3mm OD and the red is 3.5mm. 3mm is 12 AWG, 3.5 doesn't really fit.

On the engine harness, the brown ground is 4.9mm, that's 10AWG. I don't have an original red B+, but I'm guessing it's the same size or a little bit larger.

More wiring notes:

The power feed from the battery to the fuse box is 10AWG, solid black.

The headlamp white, yellow and brown are 2.6mm OD, that's in between 14 and 16 gauge. 14 gauge can carry about 15 amps at 600V.

The bulbs I will be using are HB2, which is a DOT-marked version of the H4, rated 60/55 watts. So let's call it 60 watts at 14V, that's 4.286 amps. Even assuming a 100% safety factory that's still within the margin of the factory wires. Now of course there is voltage drop and up there it won't always be 14V with the alternator running, so let's assume a nominal 12V, that's five amps, still within the safety margin.

Suppose I were to buy 130/100 Narva bulbs, 130watts/11.75 volts at the bulb (2% voltage drop) is 11 amps, with a 35% safety factory you could still get by with 14 gauge. Of course that's probably new wire with bright connections, I don't think I would risk burning the vehicle down.

[304065]

Reviving this with some new content and a question:

Does any SWB 911 equipped with Hella 128 bumper fog lamps NOT have a yellow relay above the fuse box?

I am thinking that even though the factory did not show this relay, it was there throughout the production run. 912s that didn't have fogs would not have had it or the fog wiring harness. Of course, not many cars still have original wiring. The inset photo is from an original 67S without TTG lamps.

[304065]

Gray Relay Logic

From owners manual p. 20
Light switch pushed in (lights off)- pull stalk switch- headlamps flash high beam

Light switch in position 1- parking lights- headlights flash LOW beam
Light switch in position 2- headlamps on- stalk switch normal, low beams on, stalk switch pushed or pulled, flash HIGH beam
Light switch in position 2- headlamps on- stalk switch forward, high beams on.

The place to start analyzing this circuit is the gray relay. The gray relay has two outputs-- 56a, a white wire, for the high beam, and 56b, a yellow wire, for the low beams. The gray relay's ONLY function is to implement the logic described above. It doesn't switch power in lieu of the headlamp switch, despite what the FWM claims.

With the headlamp switch in the OFF position, the relay's wiper is making contact between the high-beam output (56a) and the input (30/56). 30/56 is connected to 56a on the stalk switch. When the switch is pulled to the rear, power flows from 30 (unswitched feed from battery) to 56a, up to the relay and out to the high beams.

Looking at the diagram (and the blown-up version that's actually useful, contained in the hazard description) it appears as though the switch makes contact between 56a and 56-- but the trouble is that 56 is only powered up with the headlamp switch in position 2. I'll check the "as-built" contacts on my spare switch and correct this.

With the headlamp switch in Position 1, the parking lights are on, and the parking lamp indicator in the speedometer is illuminated. Also in this circuit (green/white wire) is power to the gray relay's coil, which pulls the wiper in so that terminal 56b and 30/56 are in continuity. This time, when the switch is pulled, the LOW beams illuminate, per the factory logic above.

With the switch in Position 2, the parking light indicator goes out, and the relay coil de-engergizes, bringing the wiper back to resting position, with continuity between 56a and 30/56. This time, when the switch is pulled, the high beams illuminate, again per the factory logic.

Why go to all this trouble? Well, probably DIN rules.

The FWM claims that the relay is used to bypass high current around the stalk switch, this is just incorrect. It says

The headlamp flasher signal is released by means of the combination switch on the steering post. The flasher relay switch is situated under the left floorboard.

The purpose of the flasher relay switch is to reduce the current load of the headlamps, i. e. , routing
the high current flow through heavy contacts in the flasher relay rather than through the switch on
the steering post.

Looking at the diagram, since the input 30/56 to the gray relay comes from the stalk switch, then all power comes through the stalk switch for both high and low beam.

[304065]

Gray:

30/56 = 30 (power)
57= 86 (power for relay coil)
85 = 85 (ground for relay coil)
56b= 87 (normally OPEN)- Low Beam, yellow- to aux Low relay 86, with 56b from the stalk switch too
56a=87a (normally CLOSED) - High beam, white- to aux High relay 86

The critical fact is that the low beam fuse gets power from EITHER 56b on the gray relay (if the parking lights are on, first notch) OR 56b on the stalk switch (if the low beams are on, second notch).

If 56a and 56b are reversed (the yellow wire is on the normally CLOSED contact, 87a, instead of 87) then 1) the high beams flash when the parking lights are on; and 2) the low beams flash when the stalk is pulled with the switch pushed in, and when the low beams are on-- just a second current path. This isn't right.

Sorry, I've had this question in my head for the last nine months since I aimed the beams.