Today I upgraded the stock map/dome lights on my 2005 mustang to Sylvania LED bulbs because one of the original halogen ones burned out. As the title suggests, both bulbs stay very dimly lit (probably 2-3% of the total output brightness) when they’re turned off. I’m sure I put the bulbs in the correct way because when I flipped them around and tried the other way, they didn’t turn on at all.
The bulbs themselves weren’t cheap about $20 for the pair and they’re from a reputable lightbulb brand, so I don’t think quality is an issue…My question is, is it normal for LED lights to do this and more importantly; will this kill my battery or is it nothing to worry about?
no it is not normal. off is off not partly off. and yes it will drain the battery. just like if you left a light on in your car and walked away for the night.
Ask your shop to measure the voltage at the sockets when they are turned off. There must be some residual voltage coming from some other circuit for the LED’s to light. It’s probably always been there, just not noticeable with the incandescent bulbs. You could remove fuses one by one, might provide a clue. I expect this is a ground problem. Make sure the ground wires for those fixtures are making good contact with the body ground.
That’s a good motivation, but the problem is the vehicle’s design engineers didn’t test that configuration. So its going to be hard to tell what the problem is, and what to do to fix it. If nothing above pans out, Tester’s idea to just install the oem replacement bulb is probably your best bet.
That is the tiny amount of current from the body computer monitoring that circuit. That itself will not drain the battery however if the body computer is sensing activity, it may not go into “sleep mode” and may discharge the battery. Let us know how it turns out.
Interestingly enough they only stay dim for about 45 minutes after clicking them off before turning off completely. Certainly 45 minutes wouldn’t drain the battery. Wonder why this is though
The body computer went to sleep after 45 minutes. The interior lights are controlled by the body computer, if you leave a door open, the lights will turn off after time via the body computer.
This is pure guess. Some dome lights dim slowly when a door is closed, which is likely to be supplied by a capacitor. Since the LED will not have the same resistance as the original bulb, the rate of discharge would be lower.
I agree with Tester: unless you frequently leave a car door open for hours, or park and read a book by the dome light, the payback time from the annual savings will be very long.
It’s leakage or monitoring current coming from the control module.
That same current was always going through the original incandescent bulbs.
(Those little interior bulbs are not halogen BTW.)
There is no additional drain with the LEDs.
Unlike the halogen bulbs, LEDs remain fairly efficient down to extremely low currents; 1% of rated and less.
I just lit a small incandescent bulb (#47) on my workbench as a test.
At 50% of it’s normal current it was down to a dull yellow glow, at 30% current a barely visible red glow.
An interesting possibility with household LED bulbs is doubling as night lights when switched off by placing a capacitor (0.1-1uF with 120V 60Hz) across the switch so the light does not go completely out.
Consumption can be 1W or even less.
Are you saying that there’s no additional battery drainage with the LED map bulbs compared to the stock bulbs even though the LED’s remain dim for a while after they’re shut “off?”
Since they both have the same current going through them?
“Some dome lights dim slowly when a door is closed, which is likely to be supplied by a capacitor.”
Maybe so in the old days, but my professional guess is that nowadays they dim the lights by having some computer (BCM?) switch the light on/off, and decreasing the duty cycle until the light appears off, and then cutting the power (except for the monitor function that somebody mentioned).
My guess is that the same current was going through the incandescent lamp, only the incandescent lamp didn’t make any visible light at that small current. One thing about LED’s is that the light’s color doesn’t change when you dim it. When you dim an incandescent light, the light output becomes more red, going from daylight to candle light. An LED lamp goes from daylight to moonlight, dimmer, but keeping the same color balance.
