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Glovebox LED Light Weirdness

 
Old 03-14-2019, 09:40 PM
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mike cap
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Default Glovebox LED Light Weirdness

So I upgraded my two interior, trunk, engine compartment, glovebox and license plate lights with the LED kit from Suncoast. Very nice upgrade and they all function fine. Polarity mattered for all except the glovebox LED which worked in either pole position.

When done I pulled the fuse that controls all these bulb locations because the car is in winter storage. I also pull the clock fuse so it doesnít run for six months needlessly. Have done this for 17 years.

The weird thing is thst when when I went to close the glovebox door with the fuse pulled - so no power to that circuit - the new glovebox LED bulb will light very dimly, like at 1/20th normal. It only lights when the door is nearly closed and I think it stays on when fully shut.

With the circut fuse installed the LED bulb acts normally and shuts off with the door. I reversed the LED and the same weird dim light. I installed the old incandescent bulb and no issue.

Any ideas? Itís not going to matter as thereís no current draw and the car lives on a maintainer anyway. Or I can just install the old incandescent bulb.

Another chapter in 993 idiosyncratic behavior. A bottle of good wine to the RL genius that figures this one out. Apologies for the long post and dull subject.
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Old 03-14-2019, 10:35 PM
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AOW162435
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Red or white?



Andreas
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Old 03-14-2019, 10:52 PM
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Red or white? Not sure what the question is.
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Old 03-14-2019, 10:54 PM
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Magdaddy
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Originally Posted by AOW162435 View Post
Red or white?



Andreas
typically red with beef, white with fish/poultry. Although I enjoy a nice Chianti with liver.
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Old 03-14-2019, 11:26 PM
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Originally Posted by Magdaddy View Post


typically red with beef, white with fish/poultry. Although I enjoy a nice Chianti with liver.
Ha! Your choice.
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Old 03-14-2019, 11:26 PM
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il pirata
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Red, Sonoma or Napa please. Actually red or white is a good question as white LED's use phosphor that is in fact phosphorescent, so they can glow for some time before going out. Have you checked after a day?
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Old 03-15-2019, 12:01 AM
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Originally Posted by il pirata View Post
Red, Sonoma or Napa please. Actually red or white is a good question as white LED's use phosphor that is in fact phosphorescent, so they can glow for some time before going out. Have you checked after a day?
Good advice I will check the hibernating 993 tomorrow. Thank you.
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Old 03-15-2019, 12:09 AM
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TheOtherEric
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I'm no EE but it may be a capacitive coupling issue, so perhaps the lines to the lamp are hot, meaning that the switch is downstream from there. If you pull the assembly and find 12v on the line even when not lit, that would explain it. If so, there's no feasible solution, but who cares if it's really pulling miniscule current.

If im correct, that seems like odd wiring by Porsche. I'd expect the switch to be upstream of the lamp so that it's not always at 12V, especially because the lamp socket is bare, unprotected. But what do I know.

p.s. If I'm correct, the incandescent bulb is pulling the same minimal current as your barely-lit LED bulb. The difference is that a tiny current will actually barely light an LED. Of course, you could measure all that to confirm.

Last edited by TheOtherEric; 03-15-2019 at 12:25 AM.
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Old 03-15-2019, 04:53 AM
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Try adding a diode, not really a cure but probably a solution?
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Old 03-15-2019, 08:23 AM
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Good suggestion Iíll check the fixture for voltage in the conditions I described.
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Old 03-15-2019, 08:51 AM
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The glove box light light switch is connected to the alarm unit, and a small current is put on the circuit to detect the opening of the glovebox. This is where the current comes from that lights up your LED bulb.
To solve this, reinstall the incandescent light bulb, use a polarized LED light bulb, or connect a diode in series of the light bulb, cathode to glove box switch.
Cheers,
Tore
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Old 03-15-2019, 09:04 AM
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Originally Posted by ToreB View Post
The glove box light light switch is connected to the alarm unit, and a small current is put on the circuit to detect the opening of the glovebox. This is where the current comes from that lights up your LED bulb.
To solve this, reinstall the incandescent light bulb, use a polarized LED light bulb, or connect a diode in series of the light bulb, cathode to glove box switch.
Cheers,
Tore
I knew there had to be a good reason for this, and it's not a surprise Tore knows it!
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Old 03-15-2019, 10:17 AM
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TheOtherEric
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Originally Posted by ToreB View Post
The glove box light light switch is connected to the alarm unit, and a small current is put on the circuit to detect the opening of the glovebox. This is where the current comes from that lights up your LED bulb.
To solve this, reinstall the incandescent light bulb, use a polarized LED light bulb, or connect a diode in series of the light bulb, cathode to glove box switch.
Cheers,
Tore
Are you saying a very low voltage is constantly applied to the glove box light? Any idea of the voltage?

And why would reinstalling the incandescent bulb solve this? Granted it wonít be visibly lit, but wonít it still draw the same current? If so, I wouldnít consider that a solution to any real issue. A dome light is one thing, but a dim glove box bulb is never seen.
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Old 03-15-2019, 10:41 AM
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ToreB
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I guess the voltage would be close to +12V without any load. However, this is applied through a resistor, and will fall to a very low value once loaded. This low current is not sufficient to light a filament bulb.

Looking from a low current perspective, the node of the bulb that normally is +12V is to be considered grounded through all the other filament lamps on this circuit.
Since the used LED is bidirectional (has an internal diode bridge or similar that makes it work in either polarity) the LED lights up due to the reversed current when glove box is closed and alarm on.

Cheers,
Tore
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Old 03-15-2019, 11:05 AM
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Tore, thanks for the info. So I guess since the incandescent bulb ihas been drawing a minimal current for all these years thereís no harm in leaving the LED bulb in place? Iíve checked this issue with the alarm disarmed of course.
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