Electrical Fault MERCEDES-BENZ C-Class Saloon (W204)

@user_191927 Good shout about the indicator. Yeah on some cars if you leave the indicator stalk in a certain position it keeps the park lights active, happened to me once after I bumped the stalk getting out.

I'd check the ground connections first mate, especially if it's an older car. Front park lights usually ground through the fender or valance and rust/corrosion can cause weird electrical gremlins like lights staying on. Friend of mine had his battery drain three times before we found a corroded ground wire behind the headlight assembly

@user_154797 Could also be the headlight switch itself is faulty. Even with everything "off" a bad switch can send power to the park lights circuit. Try wiggling the light switch next time and see if the lights flicker or go out - that's usually a dead giveaway

@lee____white Totally agree on the ground issue, had exact same problem on my old van. Cleaned up all the ground points with sandpaper and some contact cleaner, problem sorted

Another possibility - check if your door sensor is playing up. Some cars think a door is still open even when locked, which keeps certain lights on. Quick test is to look at your dash when the lights won't turn off, see if the door ajar warning is lit

@user_191927 had it right, I reckon. I accidentally left my indicator slightly engaged once after parking, came back 6 hours later to dead battery. Felt like a right idiot but lesson learned

@jeffreyOsborne23 Yeah the switch going bad is more common than people think. My neighbor replaced his entire light switch assembly for like 30 quid and fixed the same draining issue​

@user_154797 Before you start pulling things apart, double-check the obvious - is the headlight/park light knob actually in the full off position? Sometimes it gets turned just slightly and you don't notice. Saved me a trip to the garage once when I realized I'd bumped it getting my shopping bags out lol

Had this nightmare last winter. Turned out to be combination of dodgy switch AND bad ground. Fixed the ground first which helped but lights still stayed on dimly until I replaced the whole stalk mechanism

@dennishudson That door sensor thing is sneaky, happened on my cousin's car. All doors closed properly but the sensor was knackered, kept the BCM thinking boot was open so parking lights stayed active. Took ages to diagnose