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- Bone
- Member Since: 07 Feb 2026
- Location: Sussex
- Posts: 3
WARNING: Condensation in rear lights
Just a heads up to anyone that sees condensation inside their rear quarter tail light.
Don't ignore it and think it'll be okay, it might cost you a small fortune (don't ask me how I know !)
I had been casually ignoring signs of condensation for a few months, we have all had condensation inside a light fitting right?
The other day after being followed by a pal, he told me your brake light is out on the back, and sure enough he was 100% and it had failed on the offside.
No problem I thought, I'll change the bulb. NOPE, that is not an option, the whole light fitting is a sealed unit and not user serviceable. Okay I thought, lets take it indoors and dry it out, might come around if I can get rid of the moisture. So I duly pulled out the interior panel (where the jack is stowed, removed the jack, found the electrical connector and the two 10mm nuts that attach the light unit).
The light unit was put indoors in the warm for 24 hours until all signs of moisture were driven out of the unit, there are actually plenty of holes through the rear of the case, behind a foam pad where the bolts and wiring are located.
Whilst the light unit was drying out I checked the electrical connector on the car with a multimeter, and yes there was a 12v signal when the brake pedal was pressed, so the fault definitely in the light unit.
On refitting the now dried unit, bad news, still no brake light.
At this point I knew I was in the saddle for a replacement unit, I was not prepared for the cost
Holy Smoke - £400 for a brake light bulb
Since the original light unit was toast at this point, some destructive disassembly followed to investigate further, there is actually a glue joint right around the perimeter of the casing, which pried apart with some damage to the plastics. It became obvious the condensation was caused by about 10mm of water that had collected in the bottom of the housing and the brake light PCB had been immersed to the point that is was completely destroyed. The PCB track were completely corroded away, and the 'top' of the connecting cable was also badly corroded where it joined the main PCB. Most things I can McGyver a repair to, but this was beyond my abilities, the PCB with a number of through holes and minute tracks was not going to be saved.
So, what is the point of my rambling ?
If you see condensation in one of these light fittings, don't leave it and think it'll be alright. Get the unit off the car and thoroughly dried out, you might save yourself £400 for a brake light bulb ! -
- Mole HD
- Member Since: 18 Nov 2024
- Location: Orkney Islands
- Posts: 727
You've got me paranoid now.
Great tip about removing the light unit to dry it out before the condensation gets ankle deep though Bone...
With the permaseal glue on the sealed light unit...an old trick with headlight units was to pop them in the oven for 12-14 minutes. (gas mark 6 or 200° Fahrenheit.) It softens the glue and you can prise the thing apart with relatively little effort... Also without having to replace the glue for reassembly...just heat it back up until the permaseal glue is tacky and clap the 2 parts back together...
Place the light unit in the oven on a piece of wood...don't use your wife's favourite baking tray, it'll come to blows, trust me.
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