Glovebox LED Light Weirdness
03-15-2019, 11:14 AM
#16
Rennlist Member
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
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
03-15-2019, 11:38 AM
#17
Advanced
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
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
03-15-2019, 01:50 PM
#18
Rennlist Member
03-15-2019, 02:13 PM
#19
Rennlist Member
Removing it, or having a blown bulb will of course not affect alarm operation.
Cheers,
Tore
Cheers,
Tore
Last edited by ToreB; 03-15-2019 at 05:13 PM.
03-17-2019, 03:06 AM
#21
03-17-2019, 03:33 AM
#22
I had this problem on the second 993 we purchased. Lots of testing and I used Tore's guide to chase down the problem. Eventually I removed the glove box and found an unknown Lojack unit installed above the glovebox. When I removed it I realized the installer had reversed the wiring between the plunger switch and the glovebox light. Reversal of the connectors permanently corrected the problem and eliminated a frustrating battery drain.
Cheers
Cheers
04-24-2021, 08:45 PM
#23
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
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
Currently getting 0v when closed (as expected), however only +8V when opened.... Checked the connectors and everything looks OK?
Could this be related to the alarm/immobilizer as referenced above? 1997 US model.
TIA!