Had problems with my towbar electrics when I plug caravan in had strange faults on car door open etc. Traced wireing and they took a 20 amp feed of one of the boot bulbs on passinger side now both boot lights don't work checked all fuses all ok what part does the boot loom go through the car as maybe worth cutting loom at front and solder a new boot light loom in

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That's the wire I have to trace

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The red and blue wire supplies power from the interior lighting control unit to the boot lights. The controller is supplied by a 5A fuse, F3.

 

The same unit feeds power to the glovebox light and the switches on the dash etc so see if these are lit.

 

Putting a 20A fuse on a feed from an electronically switched supply is not a good idea as it could overload the switching transistor and cause damage. Hopefully, in this case, the 5A fuse in location F3 will have blown first, and the 20A fuse is adding nothing as protection.

 

The boot lights are electronically switched so that the lights can be turned off if you should leave the boot open for too long. You may have noticed too that the lamps "blink" after few minutes of having the boot open as the system starts its long time down (from memory it is about one hour).

 

Summary;

Check Fuse 3 in the passenger compartment fuse box.

Check other lights as above.

Could be the interior lighting control unit is goosed but may need more tests to be sure.

 

 

 

Wearing my professional hat, here are some general notes on fusing that may help others:

 

Fuse ratings (current rating and speed of operation) from a supply are chosen to protect the onward cable from fire under overload conditions. This is their only purpose.

Loads (such as a radio) have their own individual fuse inside to protect against damaged by an internal short that would not blow the supply fuse before internal damage is caused.

Loads such as bulbs don't need an additional fuse as they can only cause a short on the cable and this is protected by the cable fuse.

Cigar(ette) socket plug-ins have a fuse in the centre pin (often a 1 Amp glass fuse) to protect the load and more specifically, to protect the lower current rated cable that is attached to the plug-in component.

 

You can see from the above why you should never put in a bigger fuse than the original - you risk overloading the cable.

Worst of all, I have seen people recommending running a cable direct to the battery. This is how car fires can start as the cable melts when shorted to the car body due to high battery (un)limited current. 

 

This is one of the reasons I like to install tow bars myself person who had car before me had it from new so will contact him to find out what company installed the tow bar. All interior lights work but can't remember if glove box light works will check that out today. When I wire a permanent live from the battery I always have it fused as close to the battery as possible. If it is the lighting module can that be replaced with no coding etc. Also you say about it switching on the dash do you mean lighting it up or turning on mileage etc.

Also thank you for your help

Just had a Google is light module a stand alone Ecu or part of a main Ecu

Just found fuse layout obv wrong way round but there is a fuse 35 is that the main power feed for a tow bar if fitted with a proper kit and if so is that feed already to the boot or do you pick that feed up from the fuse box.

Got to bottem of it today if your octavia boot light don't work and fuse is ok and bulb ok I found the relay bunt under the drives side dash it's not really a relay as it has resistors and diode fitted and mine was destroyed boot is fed by a red wire with blue stripe

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Hi guys,

 

I have a Skoda Octavia (2002, 315 000 km) that had a trunk light issue since at least 8 years. The "door open" visual warning in the dash board did not work neither, when opening the trunk.

What I did:

- The trunk light is negatively switched off by the trunk door switch so I checked if the permanent 12 volts going to the light was OK: it was OK (with a tester, I put the positive on the red wire of the light and the negative on a good bolts in the car metal)

I checked the fuse: OK (it’s the same than the inside light)

-          I tested the door switch with an electric tester:  it was OK (I disassembled the lock to access the micro switch, put the red wire of the tester to the brown and black wire, the black wire of the tester to the other wire, when I pushed the micro switch button the resistance is infinite, when I release, the resistance is weak so the current goes through indicating that the switch works).

-          I tested with the electric tester if the current go through the brown and black wire between the light and the micro switch connector: no current. Ah!

-          I checked were this brown and black wire could be cut, and bingo, the connector was rusty and the brown and black wire cut! I just did a quick and dirt reparation like on the picture, and now the light works perfectly

-          I hope it can helps

-          Mickaël