Rear Jerrycan Holder Wiring Problem

[Big Bug]

Just wondering if someone can help. I have fitted a rear tow bar attached jerry can and spare tyre carrier. The number plate has to be mounted on it and the number plate light doesn't work. I have the 13 pin Euro to 7pin flat trailer adapter and the wiring for the number plate light plugs into the 7 pin.

With this carrier you are able to tow a light trailer at the same time so there is a socket for the trailer plug to plug into as well as run off to the carrier's number light. All the wiring is ok as I have checked it quite a few times. I see in the converter cable from 13 pin to the 7 flat plug that the black (reversing) wire and the brown (rear lamps etc) each has a diode and the black goes to pin 7 (not pin 2) with the brown.

It is a LED light but I have tried a normal one and that doesn't work either. I feel it must be something to do with the diodes and switching off the reversing sensors but can't figure how to get around the problem.

My only solution at the moment is to buy a small self contained battery light as a temporary measure. Any help gratefully received, Thankyou.

Bruce CQ

[Hillbilly]

Bad earth from the carrier to the car maybe

[Sunny43.5]

Is the carrier a permanent fitting or only for trips , I would imagine if permanent to extend the original wiring from the original number plate to the new location . by the sound of what you have done so far it may have played havoc with vans can bus system . If you add additional lights to these vans they seem easy to trip an overload .

[Umai Naa!!]

Run a completely seperate fused circuit off the battery, on it's own switch. Or you can trigger a relay off the headlight circuit.

[Big Bug]

Thanks for the replies.
Bad earth--- possible but I don't think so as the light has +ve and earth wires running to it and when the trailer is plugged in it works fine.

The intriguing part is that when the trailer is plugged in to the extension to the carrier the number plate light works fine but not when the carrier is just used by itself.

The carrier is just for longer trips so will be pulled off at home.

My brother-in-law suggested separate wiring too. Might be what I end up doing. His BMW motorcycle has can-bus and when he added his camper trailer he had to put a micro switch in each leg for it to work the lamps.

The wonders of modern technology, has me totally baffled.

Thanks again

Bruce CQ

[Sunny43.5]

As Umai suggested relays would be a safer option no chance of a false reading to the can .

[Big Bug]

As Umai suggested relays would be a safer option no chance of a false reading to the can .

That's probably what I will end up doing.

Seeing as my trailer works fine maybe another way could be to turn the tyre carrier into a "trailer" by adding stop, tail and indicator lights to it.

Thanks to all.

Bruce. CQ

[The_Hawk]

just thinking out loud here...

Given the trailer plug on the VW has some smarts built into it, is it not activating at all when it's just the carrier plugged in since it's only running the number plate light? ie is it too smart for it's own good and not acknowledging anything is plugged in?

That would explain why it all works when a trailer is plugged in since it then "sees" the trailer and everything works.



I figure you have a couple of options here, you can either extend the wiring....

If you want to hardwire it in, I'd probably just tap off one of the tail lights to run a small LED or two. They *should* be low enough draw that it won't effect the CANBUS bulb out warnings or cause other funky issues by adding them in. I'd probably add in an inline toggle switch to turn that on/off with an appropriate connector plug. Either hard wired under the back or stowed away in the boot space and just run out the back door when needed).



... or get a little creative...
LED's last forever... so you could have a battery powered LED and turn in on those few times you need it, which would mean remembering, and lets face it... how likely is that?

You could butcher up a couple of cheap solar LED path lights and wire them in! They have a light sensor so only come on at night, usually have a power switch so you can turn them off when they are stored and they charge themselves (although if you store them in a shed/garage that could be problematic). They usually run on standard AA batteries too so you can always add in extra capacity if you need longer run times.



I like to tinker...

[Sunny43.5]

I like the way you think Hawk , clever idea about the solar light .

[Big Bug]

I could just run it off the battery in the back that runs the fridge and with my panels on the roof there wouldn't be a problem.

But I tried something different just now. Yesterday I bought one of those load resistors to try and put it across the number plate light, nothing. Just before I tried putting it across the left indicator pin and earth, the number light consistently came on after 3 or 4 seconds BUT only with the engine running, not consistent with engine off. Remove the resistor and the light stayed on.... Worked on left or right not sure about the other pins.

So I think that is my easy solution for now and I will see how it goes...

I saw online the statement "do you know the difference between CAN bus and a school bus? Well don't worry, your not alone" I have learnt something, I can't mess with it.....

Thanks to everyone for all the help, much appreciated.

Bruce CQ