 | Home > Technical > TD5 110 brake lights won't work |
 
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| Chicken Drumstick Member Since: 17 Aug 2020 Location: Near MK Posts: 860  
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Logically, if there is power to the correct terminal and the Earth is good, then it can only be the bulb.
If the bulb works, are you 100% sure you are fitting the bulb correctly and that you have been checking the correct contacts? |
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20th Mar 2025 5:37pm |
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| mattsccm Member Since: 11 Jul 2022 Location: Glos Posts: 12 
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Yeah. Damn sure. Am standing there with a test light and that works and bulb that doesn't but checks fine in the other car. Just got to be the bulb holder. As it is a relatively new vehicle it has a silly little fine pinned connector hard wired to the loom and the to the bulb holder so it is tricky to swap in something else such a proofed bulb and holder combo. Old model with bullet connectors were easy to swap.
I am wondering about cutting into the loom behind the connector and using a decent junction box to put a tested holder in there. Or run a wire straight from the fuse box ! |
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20th Mar 2025 6:16pm |
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| Julie Member Since: 07 Oct 2017 Location: Nantes Posts: 570  
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Check the light switch in the black box above the brake pedal.
There is a small plastic cylinder getting in contact with the pedal arm. If it's stuck or blocking, it won't come out and brake lights won't work. https://www.auto-doc.fr/quinton-hazell/12713279 Some WD40 on it may help you out for a few days... it definitely needs replacement ... |
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20th Mar 2025 10:16pm |
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| mattsccm Member Since: 11 Jul 2022 Location: Glos Posts: 12
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First thing I did and it is fine. I am actually testing it all by bypassing the switch as it is more effective than propping the brake pedal down with a bit of fire wood.
It has been suggested that there may be a current "leak" at a junction and enough current is getting through to the bulb holder to indicate a circuit but when 21w is needed for the bulb there isn't enough. Clutching at straws. May end up with a wire run straight to a known good earth and another to the fuse box, both to a know good bulb holder and working my way back through the look to isolate things. |
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22nd Mar 2025 9:10am |
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| Julie Member Since: 07 Oct 2017 Location: Nantes Posts: 570
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I'd replace that 15£ switch anyway (or mesure if it's in good condition)
Just to be 100% safe before I started that investigation ...  |
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22nd Mar 2025 9:52am |
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| mattsccm Member Since: 11 Jul 2022 Location: Glos Posts: 12
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Agreed and one on the way but by-passing it to test the circuit proves it is fine. Off to see what's what with a test rig beautifully made with a head shrink and great joints every where. Never been so careful!
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22nd Mar 2025 10:36am |
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| Julie Member Since: 07 Oct 2017 Location: Nantes Posts: 570
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... and don't forget the trailer light pick-up which is good source for faults, too
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22nd Mar 2025 11:29am |
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| mattsccm Member Since: 11 Jul 2022 Location: Glos Posts: 12
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Well, it's done. Went back painstakingly through the loom from each side. Bypassed the junction box where things stopped working and pulled that apart. What looked fine actually had a broken pin. It could in theory make contact and did if you whacked it closed but wiggled loose. Had something more robust in the shed so replaced the junction with that. Job is done and I even got round to wiring in the high level brake light as well! Thanks all
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22nd Mar 2025 2:22pm |
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