FAQ
TL;DR: To sync footwell LEDs on a Golf 4, tap the dome‑light circuit and add a 12V manual feed with a diode—"provide +12V through the switch" to stop backfeed. This preserves fade‑out and adds a driver‑operated mode. [Elektroda, Anonymous, post #17147154]
Why it matters: This helps Mk4 Golf owners add footwell LEDs that follow factory fade while retaining a safe, convenient manual ON/OFF.
Quick Facts
- Electrical feed: route +12V through a switch and a rectifying diode to prevent backfeeding the cabin lamps. [Elektroda, Anonymous, post #17147154]
- Diode sizing: a 5A rectifier is typically sufficient for short LED strips; higher‑amp options exist. [Elektroda, Anonymous, post #17147228]
- Dome‑light harness (documented case): yellow‑green used as LED +, blue as dimming return; tying brown to blue backfed and lit the cabin. [Elektroda, Jaznbu, post #17146824]
- Fade behavior: “The LEDs will also dim” when tied into the interior light circuit. [Elektroda, Anonymous, post #17146590]
- Timing: the cabin lamp fades after approx. 25 seconds or at key‑on. [Elektroda, Jaznbu, post #17135309]
Where’s the Golf 4 interior light “dimmer”—is there a module to tap?
The Mk4’s courtesy fade is built into the interior lighting circuit, not a separate module. You don’t need to find a standalone dimmer. Tap the dome‑light harness so your LED strip powers up on door open and fades on door close. [Elektroda, Jaznbu, post #17146824]
Which wires do what at the headliner lamp?
In the documented case: yellow‑green fed the LED positive, blue served as the dimming return (negative), and tying brown to blue backfed the cabin lights. Verify with a multimeter before final connections, as looms can vary. [Elektroda, Jaznbu, post #17146824]
Will LED strips actually dim with the Golf’s fade‑out?
Yes. When wired to the dome‑light circuit, LED strips follow the OEM fade. As one installer put it, “The LEDs will also dim.” Match polarity during testing to confirm the effect. [Elektroda, Anonymous, post #17146590]
Why do my LEDs switch off earlier than bulbs during dimming?
LEDs need a minimum forward voltage to conduct. As the fade lowers voltage, the LED goes dark once below that threshold. “The LEDs will go out earlier than the bulbs… because they have a specific ‘ignition’ voltage.” [Elektroda, Anonymous, post #17141876]
How do I wire the strip so it fades with the cabin light?
Use the dome‑light connector.
- Connect LED + to the dome‑light feed used by the courtesy lamp.
- Connect LED − to the lamp’s dimming return/ground.
- Open and close a door to confirm it lights and fades.
[Elektroda, Jaznbu, post #17146824]
How can I add a manual ON without lighting the whole cabin?
Feed LED + through a switch from constant or accessory +12V and place a rectifying diode in series. The diode acts like a check valve, blocking backfeed to the cabin bulbs when you switch the strip on manually. [Elektroda, Anonymous, post #17147154]
What diode rating should I choose?
Use a 5A rectifier diode for short footwell strips. It adds headroom and runs cool. “If you buy 5A… it shouldn’t even heat up.” Larger diodes, like 30A units, also work if on hand. [Elektroda, Anonymous, post #17147228]
Which way round do I install the diode?
Put the diode between the manual switch and the LED +, with the band toward the LED. If the strip does not light in manual mode, reverse the diode. Reversed orientation won’t harm anything; it just blocks current. [Elektroda, Anonymous, post #17147345]
What switch setup gives Door/Off/On control?
Use an SPDT ON‑OFF‑ON switch. Connect the center to LED +. Connect one outer terminal to the “dimmer” + from the dome light, and the other outer terminal to a constant +12V. The center position turns the strip OFF. [Elektroda, Anonymous, post #17148387]
Where should I take the manual +12V feed from?
Use the radio’s +12V supply or the cigarette lighter. Many prefer the radio feed, because removing the key cuts power even if the switch stays ON. This reduces the risk of drain. [Elektroda, Anonymous, post #17147345]
My test lit every cabin bulb—what went wrong?
You backfed the interior lighting. Tying the brown wire to the blue return made all cabin lights turn on. Fix it by using the proper dome‑light lines and isolating your manual feed with a rectifier diode. [Elektroda, Jaznbu, post #17146824]
Can I isolate both the dome‑light feed and my manual feed?
Yes. Diode‑OR the two +12V sources into LED +. Place one diode in series with the dome‑light feed and another in series with the manual +. “With two [diodes]… both the lamp and the radio will be cut off from each other.” [Elektroda, Anonymous, post #17147449]
How long does the Golf 4 cabin lamp stay on before fading?
About 25 seconds, or it fades immediately when you turn the key. This is the observed factory timing for the Mk4 Golf dome light. [Elektroda, Jaznbu, post #17135309]
Will my LED strip follow the key‑on fade if wired at the lamp?
Yes. When connected at the headliner lamp, the strip lights on unlock and dims after the doors close, following the cabin lamp’s behavior. Confirm polarity and dimming with a quick door test. [Elektroda, Jaznbu, post #17146824]
