OEM T6 LED Rear Lights With Sequential LED Indicator "retrofit"

OEM T6 rear LED lights are factory equipped with 16W filament bulb for indicator.
My LED sequential strip take 0.33A, which translates to 4W.
This is obviously short by 12W to expected 16W and results with hyperflash and double frequency click in the instrument cluster.

Available coding adjustment for indicator setup is as follows
BCM 09, Byte 18
bit 3&4 = front/rear/side
00 = 21/21/5 W
01 = 21/27/5 W
10 = 21/16/5 W
11 = 27/27/5 W
The lowest possible setting is "10" which I had already as a factory setup so the only solution was to add extra resistor.

Quick maths:)
Required indicator additional power(wattage) = 16W - 4W = 12W

P = U x I ---> I = P / U = 12W / 12V = 1A ===> R = U / I = 12V / 1A = 12Ω

So the selected resistor was 12Ω and for sufficient heat dissipation 50W seems to be sufficient.
RS PRO Panel Mount Resistor

CBCA73FA-70A4-411C-9E4D-F3E0827D7A73.png

Credit to @Loz for resistor type and resistor layout inspiration.

@Robert just a quick one - my resistors have arrived and I just want to check I’m splicing the correct wires.

Is it the two that are beside each other (wires 1 and 2, with 4 being left alone)?

33C75895-B4E8-4F30-B8AA-07E6F5575254.jpeg

That’s what it appears to be, but your image resolution has been downsized.

47959A36-18CB-400B-A4C8-1AB9B06B91F5.jpeg

(I’ve soldered the LEDs to male wedge connectors)
 
I have not started this project yet, so i was just going to get my multimeter on the pins and work out which one had voltage when the indicators are flashing. You only need to add the resistor in-line on the positive led. Where did you get the blue wedge connectors from and do they fit into the bulb holder ok?
 
I have not started this project yet, so i was just going to get my multimeter on the pins and work out which one had voltage when the indicators are flashing. You only need to add the resistor in-line on the positive led. Where did you get the blue wedge connectors from and do they fit into the bulb holder ok?
Extra resistor has to be added parallel to the LED stripe and not in series. Obviously resistor value (ohm) should be calculated based on the wattage of your LED stripe.
 
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@Robert just a quick one - my resistors have arrived and I just want to check I’m splicing the correct wires.

Is it the two that are beside each other (wires 1 and 2, with 4 being left alone)?

View attachment 67872

That’s what it appears to be, but your image resolution has been downsized.

View attachment 67871
(I’ve soldered the LEDs to male wedge connectors)
I don't remember mate.
Hopefully I will find some time this evening and get it verified for you;).
 
Extra resistor has to be added parallel to the LED stripe and not in series. Obviously resistor value (ohm) should be calculated based on the wattage of your LED stripe.
Sorry you are right, my mistake. The resistor needs to be across the load (led strip) to increase the resistance. I will know more once all my bits arrive...
 
@Robert just a quick one - my resistors have arrived and I just want to check I’m splicing the correct wires.

Is it the two that are beside each other (wires 1 and 2, with 4 being left alone)?

View attachment 67872

That’s what it appears to be, but your image resolution has been downsized.

View attachment 67871

(I’ve soldered the LEDs to male wedge connectors)

@Ads_Essex sorry for delayed reply.
Life is busy sometimes;).
Connect your extra resistors like this.

20200501_200627.jpg
 
As I have mentioned before(somewhere else;)) some sequential LED strips are voltage sensitive.
For example they work perfectly with 12V DC and then they misbehave with increased voltage of 14.5V DC(when engine is running).
Luckily these strips are very rare and majority of recent/modern strips cope very well with increased voltage.

Then there is another trap :whistle:.
Indicator's pulses can be PWMed(Pulse Width Modulated) and this is controlled by BCM coding.
Almost all aftermarket LED strips don't like PWM and they won't work properly, especially when engine is running.

This is how indicator pulses look like when PWM is ON and engine is running.

20200501_195612.jpg

And this is how indicator pulses look like when PWM is OFF and engine is running.

20200501_195908.jpg

To deactivate indicator PWM the following VCDS coding modification needs to be applied.
09 BCM, (Byte 19, bit 3) = 0 (unticked)

20200501_1948000.jpg
 
@Ads_Essex sorry for delayed reply.
Life is busy sometimes;).
Connect your extra resistors like this.

20200501_200627-jpg.68149
No need for an apology.
You’re a gent. Thanks mate, appreciated
 
Sorry you are right, my mistake. The resistor needs to be across the load (led strip) to increase the resistance. I will know more once all my bits arrive...
We are not trying to increase the resistance but actually to reduce it.
And by reducing the resistance we are "forcing" more current to be produced by BCM output and this way the BCM thinks that there is no fault cause expected wattage is being consumed.
 
Has this happened to you? Do you know where these LEDs were installed?
Yes, those were mine. I had them in a T6 in cargo room roof lamps (replacing the regular bulbs). After a few weeks the smoke came out.

Before installing them I had tested them on a bench. Had them turned on more than 20 hours at different voltage levels (10, 12.5, 15 V) to verify they won't warm up excessively - as they have some fancy electronics. Obviously need to add a test point into my procedure :geek:

However, can't exclude the infamous BCM on early T6's - which probably didn't shut down properly as at the worst starter batteries were flattened. Was eventually cured by a BCM software update.
 
Should i turn off pwm with the above coding if fitting normal led’s in the rear lights?
 
Should i turn off pwm with the above coding if fitting normal led’s in the rear lights?
You don't have to do that but note that some LEDs don't like PWM and you might end up with failed bulb.
See @mmi's post above.
 
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You don't have to do that but note that some LEDs don't like PWM and you might end up with failed bulb.
See @mmi's post above.
Seems like the safer option to turn it off, would it have an effect on anything else? Can you recommend a resistor as well please as I've fitted LED indicator bulbs in the rear, they work perfectly but i have fast flash on the dash!
 
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