Can someone tell me what this wire is for or how this works?

[danny01975]

82GK. I installed an LED flasher and it works fine with my LED bulbs. The self cancelling doesn't work, as expected. But that's a trade off I'm willing to accept to have much brighter signals and longer lasting LED bulbs. I can turn the signals off myself. I connected it using the O/G for power, and the Lbl for signal back to the stalk controller and out to the lights. All good.

But what does the B/Bl wire do? I assume it has something to do with communication to the TSCU. Also, if the TSCU is just telling the relay to turn on or off, why can't it also do that with an LED flasher?
Screenshot 2025-01-31 at 6.26.58 AM.jpg

Coincidentally, when testing the stock flasher, probing the B/Bl wire terminal with a test light connected to ground causes relay makes a slight buzzing sound and stops flashing. Maybe the TSCU is just sending the B/Bl wire to ground when the timer is done, effectively stopping the flasher?

[danny01975]

Update.. So while doing some testing, I think I've got it mostly figured out. The orange wire is constant hot to the relay, and the light blue sends the flashing signal to the turn signal switch, then out to the lights. The flasher is in a "constant ready" state to start flashing.

When the signals are off the TSCU is sending 10v across the B/Bl wire. Which disables the flasher. The flasher is probably has a normally closed relay in it. So while it has 10v applied to the terminal, it remains open, and disabled. When you switch to positions 1 or 5 you send a signal (12v) to the TSCU over the Lg/B wire. The TSCU then removes the voltage from the B/Bl wire, which closes the relay and allows the flasher to start working. Because your turn signal switch is in either positions 2 or 4 at this point, the flashing signal is then routed to the appropriate bulbs. Once the timer is done, the TSCU puts 10v back on the B/Bl wire, opening the flasher relay and stops the flashing.

Even with the flasher disconnected, the TSCU still goes through this procedure. I have verified this by watching the voltage come and go, as expected, on the B/Bl wire while operating the turn signals at speed. This 10v signal from the TSCU can likely be used to operate a relay that will turn the LED flasher off and on. In exactly the same way the old flasher works.

The 10v isn't constant however. When the engine revs it goes as high as 14v, and at idle can drop down to 9v. With a buck converter to keep the control voltage steady, and a 5-12v relay, I think I can get it to work WITH THE STOCK TSCU.

So the end result would be LED bulbs, LED flasher AND the stock self cancelling function.