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The front lights stopped working on my friends T4 Caravelle last week. The rear lights and front sidelights and dash lights are still functioning. It has a horrid Xenon/HID conversion but have re-made some of the connections but without getting anywhere with the job and as there is no way of testing the bulbs have drawn a blank. lifted the orange fuse and the remaining lights went out so it isnt the fuse at fault. Is there a relay or something or could it be a canbus error ?.
I don’t think the T4 had canbus so it’s unlikely that will be the issue. Can you check the wiring at the lamps to see if power is getting through. I imagine there will be some sort of relay involved in powering these headlights but given the aftermarket conversion it’s difficult to speculate where the fault may be.
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Thanks. The Caravelle is a 2003 reg model and a 2.5TDI so it may or may not be canbus - I cannot find any definitive information though I have gleaned that part of the system is canbus such as the engine and imobilizer. I have checked for voltage and there is none at the ends of the wires going to the high and low beam and the blue high beam indicator isn't showing at the dash. I need to check if there is voltage at the fuses but can't find any info on the fuse numbers relating to the high and low beam or even whether there are any relays - though I can't find any. All the fuses in the fuse box are intact as I went through every one of them checking resistance with a multimeter. I'm going to go back to original incandescent bulbs but fit relays to help reduce the voltage drop that makes the standard system so weak.
See if relay 4 is OK: Fuse box Volkswagen Transporter T4.
The high-beam indicator is straight off of the same supply as to headlamp, so no surprise they are both not working.
Also maybe F1 / F2 / F11 / F12 - but unlikely all would blow.