LED Brake Lights

[spoke]

Here's a 911 (pre '74) parking/turn signal assembly. I was asked if I could fit an LED board in a pre '74 front turnsignal assembly. I thought I could. And here it is on my kitchen table. Looks like I'm making a pre '74 front turnsignal LED board.



This board will have LEDs mounted at an angle so they point to the front of the vehicle. This is done by using spacers during soldering and bending to the correct angle with RTV to hold the LEDs in place.

I think this is the angle the assembly would be mounted on the car. The lines look consistent.

[RDM]

Originally Posted by spoke

Cruise does have some current drain into ground via the bulbs. Have you run your cruise control after putting in the LEDs? I have to find out how much current is draining into the LEDs so I can add appropriate ballast resistors on the boards.

I've been putting ballast resistors on all the turnsignal boards that I design. I've found some LED-ready flasher relays that need at least some resistance in the load to start flashing.

I haven't used the cruise control since I learned how to turn it on and tested it back when I bought the car.

[spoke]

Here's the pigtails I sent to Keith and Dave to test the cruise control input current. It's also instructions on what to test.

Simply these are resistors which are connected to brake and ground. Careful with the red wire as this is your fused brake light circuit. Do not hit the brakes when this is attached.

One resistor is 100 ohms and the other is 3.01k ohm. Two tests to do with each pigtail with ignition on and no brakes:

1) Remove only one LED board; leave the others in place.
2) Plug in 100 ohm pigtail; turn on ignition or start car whichever gets the LEDs being lit.
3) In Volt setting, measure the voltage across the resistor. Current will be V/100. Note if other LED boards go dark.
4) Change to ampere setting; Touch each side of the resistor with the probes, measure the current. You will be shunting (paralleling) the resistor with the ammeter. In essence you will be shorting out brake to ground in ammeter setting but there should be no direct connection to 12V. Start out in 10A setting then to lower setting once you know it's safe to connect in ammeter setting.
5) Swap pigtails installing the 3k pigtail; turn on ignition or start car whichever gets the LEDs being lit.
6) In Volt setting, measure the voltage across the resistor. Current will be V/3010. Note if other LED boards go dark.
4) Change to ampere setting; Touch each side of the resistor with the probes, measure the current.

This information should be enough to get an idea what the impedance is looking into the CC unit brake sense lead.

[DaveMcKenz]

Ok
I will temporarily reconnect my cruise control unit and post the results.
Dave

[DaveMcKenz]

Hi Spoke,
I did your measurements several times to get consistent readings.
W/ 100 ohm pigtail 0.77 volts and 7.2 ma, all other boards went dark
W/3K ohm pigtail 7 volts and 8.3 ma, other board stayed lit.
I hope this helps you, and I can send pigtails back
Thanks,
Dave

[Porsche 2]

Spoke,
Agree with Dave exactly with my measurements on my '87 Carrera.
Cheers, Keith.

[spoke]

Guys, thanks for the measurements. It's good that both of your measurements produced similar results.

The 100 ohm resistor provides good indication of the input current. Looks like it's as you measure 7.2ma.

I would like to send 2 more resistors. I'm going to try 200 and 300 ohms. The 3.01k was too large and only served to measure the turn-on voltage of the LED boards at 7V.

I wonder how much voltage can exist on the brake light wire and the CC still operates ok.

[DaveMcKenz]

Just some more feedback. I bought an EP36 flasher on Amazon, in anticipation of installing LED turn signals. I installed it today with my old filament bulbs still in place, and it works fine, and fits fine. The terminals on the OEM are marked 31, 87 and 87a; while the EP36 is marked 31, 49 and 49a at the corresponding terminal positions. I am sure that it will work with any combination of LED and filament bulbs.
Thanks,
Dave

[spoke]

Here's the follow-up pigtail. It has five 100 ohm resistors in series and a ground wire to select different resistances. This pigtail can be configured for 100, 200, 300, 400, or 500 ohms to get the most information.

These should be in the mail tomorrow.



Here's the pigtail set to 300 ohms since the lower 2 resistors are shorted out with the ground wire.

[spoke]

I'm hoping that at minimum 150 ohms will be enough to allow the cruise control to function and keep the LED brake LEDs off. 150 ohms should drop about 1-1.5V on the brake light wire. Hopefully the CC will be happy with this.

I fitted one of the round boards with a ballast resistor of 300 ohms. With 2 brake LED boards in parallel, together they present 150 ohm impedance.

The 300 ohm resistor will burn about 0.65W with 14V input. I estimate that the additional power dissipation will add less than 5C rise in temperature.

I'm testing out this board now. I'll run the board all night to assess temperature rise. The resistor will have to fit on the top of the board but it shouldn't be in the way of anything.

[Porsche 2]

Sent you a PM.

[scotricker]

Where will I find the flasher unit in my 1978 911 SC ? I would think just up there under the dash, but I dont see it. Or, is it by the fuses/relays?

My turn signals have always flashed too quickly, and I thought I'd try the EP36 as mentioned in this thread, before getting spoke's LEDs

I've checked grounds, and super-cleaned/dremeled connections, a bunch of times.

So, where is that flasher? I'll try the EP36. thanks

[DaveMcKenz]

Originally Posted by scotricker

Where will I find the flasher unit in my 1978 911 SC ? I would think just up there under the dash, but I dont see it. Or, is it by the fuses/relays?

My turn signals have always flashed too quickly, and I thought I'd try the EP36 as mentioned in this thread, before getting spoke's LEDs

I've checked grounds, and super-cleaned/dremeled connections, a bunch of times.

So, where is that flasher? I'll try the EP36. thanks

On my 3.2, the flasher is seen in front of the fuel gauge by looking from the luggage compartment, after folding down the carpet. It looks like a 1" x 1" x 2" tall black box.
It may be different on your SC.
Good luck,
Dave

[skylark]

spoke,pm. you yesterday carl

[spoke]

Originally Posted by scotricker

Where will I find the flasher unit in my 1978 911 SC ?

I couldn't find the flasher at first then I turned on the 4-ways and followed the clicking to the flasher.

[spoke]

I tested an LED board with the 300 ohm ballast resistor by keeping it powered on brake for 48 hours. The corner of the board with the resistor was a little warmer than the other corners but not much. The whole board is a heat sink as there is a ground copper pour on both sides of the boards with many vias to connect the top ground with the bottom.

Once I can confirm the fix with the tests Dave and Keith are doing, we'll modify all boards going out. Sorry for the delay; just want to make sure the fix is viable and effective.

For those of you who have already purchased boards and would like this fix installed on your boards, if you pay shipping back to me, I'll mod the boards and pay shipping back to you.

[spoke]

Dave, Keith,

Here's instructions on what to test with the latest pigtail. This one has five 100 ohm resistors in series along with a ground (GND) tap wire.

The GND tap wire will be used to short out 0, 1, 2, 3, and 4 resistors. This will make the resistance 500, 400, 300, 200, 100 ohms respectively. At each of these settings, take a voltage measurement from the brown wire to the red wire.

Directions:
For nomenclature, we'll number the resistors R1, R2, R3, R4, R5 with R1 connected to the brown wire and R5 connected to the red wire.

To short out a resistor, just wrap the end of the GND tap wire around the resistor connection a couple of times. The end of the tap wire is tinned so it will hold in place.

Test 1: 500 ohm; do not connect the GND tap wire to anything. Car on, brakes off, measure voltage across red to brown wires. LEDs on?

Test 2: 400 ohm; connect the GND tap wire to the connection between R1 and R2; This shorts out R1. Car on, brakes off, measure voltage across red to brown wires. LEDs on?

Test 3: 300 ohm; connect the GND tap wire to the connection between R2 and R3; This shorts out R1, R2. Car on, brakes off, measure voltage across red to brown wires. LEDs on?


Test 4: 200 ohm; connect the GND tap wire to the connection between R3 and R4; This shorts out R1, R2, R3. Car on, brakes off, measure voltage across red to brown wires. LEDs on?

Test 5: 100 ohm; connect the GND tap wire to the connection between R4 and R5; This shorts out R1, R2, R3, R4. Car on, brakes off, measure voltage across red to brown wires. LEDs on?

[DaveMcKenz]

No problem. Will post results when completed.
Thanks,
Dave

[69porsche]

Will this fit in 1969. 911E? By the way, bought a Daniel Stern third brake light-best thing going, I hope your project works out to benefit all- thanks. I would be interested if available -Gordon

1967 MGBGT
1967 Porsche 912
1968 Jaguar E type series 1
1969 Porsche 911 E

[RocketWrench]

Spoke: PM sent regarding '76 911S in the UK.

Bob