[XinZhao]

My p21/5w bulb went dead (The 5w) and i decided to change it with a LED one, also on the other side where I realized that the 21w doesn't work. When i made the change - I realized that suddenly, the 3rd, top (OEM) LED light was staying on all the time, although the break pedal was released. After some time, I realized that when I press the pedal, the third (top) stopping light becomes more bright.

Can anyone explain this?

[The Gonz]

Even in my FD I need to consider the BCM's response to much lower current drawn by LEDs. Do your LEDs have the ballast loads attached (typically 6 Ohm 5 Watt resistors)?

[XinZhao]

I guess no. But I taught this isn't important because I have no notification on the instrument table when a bulb dies.

I have had the front 5w bulbs (with no balast) LED and for plate also and there were no problems

[Shambles]

This might be a classic case of a BCM reset doing the job.

Disconnect battery -ve for 30 minutes then reconnect. See if that helps.

[XinZhao]

I did it, for even more than 30 minutes. No result. I changed back to original normal bulbs and everything works fine. My guess is this - Ecu sees no current through tail lights - and so he lights up the middle one. Current for led bulbs is to small for him to register it as "fine".

[sundiz]

This is something that can happen with system not being LED compatible. I had a dimmer in my living room with old incandescent bulb. When I moved in I changed all the bulbs to LEDs. When I put the fuse back on, the light was like it had been dimmed, even it was not supposed to be on. And when I turned it on, it lighted up the room. At Off position it was on, but dimmed. Some of these light systems are desingned so that there is paracitic current drain. With incandescent or halogen it is not a problem. But LEDs light up even with the paracitic current. Also many cars need the LEDs with resistors as the system has been desingned to be working with old regular bulbs.

I changed my trunk/boot light to LED trying to get more light during dark winter time. It worked few weeks until my BCM fuse burned. Not 100% sure if it was due the LED bulb, but never had that problem with incandescent bulbs. Changed back to normal bulbs and everything has been working fine.

[BrendanP]

As far as I know the FD has conventional wiring to the rear light cluster, there's no CANbus like in the later versions, so there is no diagnosis of faulty bulbs. The bulbs should all be connected in parallel and they either get 12V to light 'em up, or nothing. If it wasn't for the covid-19 lock down I'd ask my girlfriend to bring her FD over to see if hers does the same.

[The Gonz]

Light circuits tend to do these thongs also when you end up with a bad earth connection. Check all your wiring and seating of bulbs.

[nzenigma]

My p21/5w bulb went dead (The 5w) and i decided to change it with a LED one, also on the other side where I realized that the 21w doesn't work. When i made the change - I realized that suddenly, the 3rd, top (OEM) LED light was staying on all the time, although the brake pedal was released. After some time, I realized that when I press the pedal, the third (top) stopping light becomes more bright.

Can anyone explain this?

Check the manufacturers blurb. Some LEDs are polarity dependent and you are advised to reverse the connection.
A bit tricky with a bayonet fitting.
Unless you have electronic experience, I suggest you go back to standard bulb.