Help with LED brake lights
Good day folks. I'm having an issue which has been driving me nuts for the past few days: I CANNOT get some LED brake/parker lights to work on my car. I managed to track down the issue and THOUGHT I solved it, but when I tried it again, it STILL doesn't work....it's one of those "how the hell does this work?" type of deals. *LONG STORY WARNING* 
Let's explain some stuff so we're on the same page: I don't know if I'm calling them by their right name to begin with...these bulbs have two intensities: a dim one for the parker and a bright one to indicate braking. They achieve this by employing two separate filaments inside the same envelope, nothing special or amazing there, we've all seen this. The socket is a BAY15D, so it's got two contacts on the end for the + of each filament and the shroud is the -. They look almost identical to these.
Now the LED ones I picked up also have a BAY15D socket and claim they do exactly the same thing: light up at full brightness when braking and dim down when you've got the parker lights on...fair enough I thought - should be a direct replacement and work like a charm, but no.... These weren't cheap either, so I MUST get them going or else this will be a disaster of automotive modding
When I first got them, I first tried them out on the bench, just to ensure they work before I start taking things apart: negative clamp around the base and then touched the positive to each of the terminals and sure enough they worked. Red light came on at two different levels as advertised...no problems there so it was time to try them out on the car.
After installing just one, I immediately faced unwanted behavior: I first tried the "parker mode", since it was easier to just turn the lights on and have a good look around the back, whereas with the brake I'd have to find something heavy to place on the pedal and....anyway. I got nothing on this first try: no light at all...I tried wiggling the socket around, tapping it, cleaning those contacts...it was useless...the light simply wouldn't come on. Adding to my frustration was the fact that inserting the original classic bulb which had been on the car for 10 years, resulted in immediate light, so why the hell wasn't the new one which I just tested on the bench 10 minutes ago not working ?
After many many hours of tinkering and measuring, I managed to identify what the issue was...it's the brake circuit that's killing the light when installed...how do I explain this, since this is a wall of text already ?
Check out the crude schematics I drew: when the brake is "off" (foot NOT on pedal, the car is rolling so to say), the brake wires aren't left floating: they're actually pulled low to GND, which isn't a problem for the dual-filament lamp, since the two filaments operate individually, but these LED lamps don't have two different sets of LEDs to achieve the same effect. I THINK they most likely use a simple resistor in line with the "parker" contact to achieve the dimmer light, so even though 12v were going into the lamp, they were immediately sank back into the GND through that internal resistor and the brake switch...hope that makes sense.
Ok, so what now ? Are we just gonna leave it here ? Of course not. What I tried so far (but failed) was installing a diode in series with the brake wire (not figured in the schematics), hoping that when the brake is "off" (NOT pressed down), I'd get no current flow from the parker wire back through the resistor and into GND through the brake switch. I first simulated the setup on the bench: ground clamp around the base again and sure enough, when the parker is lit and the other contact is grounded, it immediately kills it. Installing a diode in series with the brake contact worked: grounding the wire no longer shut the light off and when it was the brake's turn to light up it did. With high spirits, it was back at the car again, where frustration resumed: with the diode in place, the parker light does come on, since the diode indeed blocks the current from going into GND, but now the BRAKE doesn't come on....UUGH ! WHY ?! Again, it worked on the bench, why not the real deal ?! When I touched the "enabled" brake wire with the diode to the corresponding contact, it made no difference: the lamp didn't come on any brighter.
My only guess is that the brake lamp on the other side has something to do with it, since I haven't tried changing both at the same time - I only tried one so I wouldn't have to do twice the work if it didn't work *pun intended*....what now ? Is the diode to blame ? It's an SB5100 I reckon. I shall try unplugging the opposing light to see if it changes anything...if it doesn't then God knows what we'll do...looks like we'll have to build a little transistor switch or something....Cheers guys and thanks for your patience.
Let's explain some stuff so we're on the same page: I don't know if I'm calling them by their right name to begin with...these bulbs have two intensities: a dim one for the parker and a bright one to indicate braking. They achieve this by employing two separate filaments inside the same envelope, nothing special or amazing there, we've all seen this. The socket is a BAY15D, so it's got two contacts on the end for the + of each filament and the shroud is the -. They look almost identical to these.
Now the LED ones I picked up also have a BAY15D socket and claim they do exactly the same thing: light up at full brightness when braking and dim down when you've got the parker lights on...fair enough I thought - should be a direct replacement and work like a charm, but no.... These weren't cheap either, so I MUST get them going or else this will be a disaster of automotive modding
When I first got them, I first tried them out on the bench, just to ensure they work before I start taking things apart: negative clamp around the base and then touched the positive to each of the terminals and sure enough they worked. Red light came on at two different levels as advertised...no problems there so it was time to try them out on the car.
After installing just one, I immediately faced unwanted behavior: I first tried the "parker mode", since it was easier to just turn the lights on and have a good look around the back, whereas with the brake I'd have to find something heavy to place on the pedal and....anyway. I got nothing on this first try: no light at all...I tried wiggling the socket around, tapping it, cleaning those contacts...it was useless...the light simply wouldn't come on. Adding to my frustration was the fact that inserting the original classic bulb which had been on the car for 10 years, resulted in immediate light, so why the hell wasn't the new one which I just tested on the bench 10 minutes ago not working ?
After many many hours of tinkering and measuring, I managed to identify what the issue was...it's the brake circuit that's killing the light when installed...how do I explain this, since this is a wall of text already ? Check out the crude schematics I drew: when the brake is "off" (foot NOT on pedal, the car is rolling so to say), the brake wires aren't left floating: they're actually pulled low to GND, which isn't a problem for the dual-filament lamp, since the two filaments operate individually, but these LED lamps don't have two different sets of LEDs to achieve the same effect. I THINK they most likely use a simple resistor in line with the "parker" contact to achieve the dimmer light, so even though 12v were going into the lamp, they were immediately sank back into the GND through that internal resistor and the brake switch...hope that makes sense.
Ok, so what now ? Are we just gonna leave it here ? Of course not. What I tried so far (but failed) was installing a diode in series with the brake wire (not figured in the schematics), hoping that when the brake is "off" (NOT pressed down), I'd get no current flow from the parker wire back through the resistor and into GND through the brake switch. I first simulated the setup on the bench: ground clamp around the base again and sure enough, when the parker is lit and the other contact is grounded, it immediately kills it. Installing a diode in series with the brake contact worked: grounding the wire no longer shut the light off and when it was the brake's turn to light up it did. With high spirits, it was back at the car again, where frustration resumed: with the diode in place, the parker light does come on, since the diode indeed blocks the current from going into GND, but now the BRAKE doesn't come on....UUGH !
WHY ?! Again, it worked on the bench, why not the real deal ?! When I touched the "enabled" brake wire with the diode to the corresponding contact, it made no difference: the lamp didn't come on any brighter.My only guess is that the brake lamp on the other side has something to do with it, since I haven't tried changing both at the same time - I only tried one so I wouldn't have to do twice the work if it didn't work *pun intended*....what now ? Is the diode to blame ? It's an SB5100 I reckon. I shall try unplugging the opposing light to see if it changes anything...if it doesn't then God knows what we'll do...looks like we'll have to build a little transistor switch or something....Cheers guys and thanks for your patience.
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