Technical Problems with towbar electrics

[oinklet]

Hi all, please excuse any inadvertent breach of etiquette.

I had a Witter towbar fitted to my 2007 Panda multijet , and all worked fine until one particularly torrential downpour. Now the lights on my trailer do not work, and a borrowed lighting board does nothing either.

I'm more than a bit ignorant about car electronics, but presumed that the fuses would be a good place to start, but I am stumped.

I've opened the fusebox on the drivers side, but I'm not really sure what I'm looking for: The first row of small fuses, marked F19 under the battery connection down to F87. In the manual it give F15 four slots down from the top as "Trailer unit" but this slot is empty. Four slots up from the bottom is F20 which is shown as "Fuse available". There is a fuse here (15 amp), but looks intact to me.
(Originally I had a marked photo, but I have too few posts to be allowed to put it here.)

Edit - whoops, seemed it didn't mind the attachment after all. The orange circle marks the empty slot F15 marked as "Trailer unit"
The Mauve circle shows the F20 slot marked as available but filled with a 15 amp fuse.

Am I barking up the wrong tree here, and does anybody have any suggestions what I should be looking for, and where?

Any help appreciated.

 

[Goudrons]

I doubt the fuse for the towbar electrics will have been routed via the fuse box.

Unless a complete knob has fitted it, there will be a fuse on the relays power wire, somewhere between the relay (in the boot somewhere) and where ever it's picking up it's 12v. (battery?)

You need to start either at the battery and look for a single wire connected to the + terminal and follow that, the fuse should be near the battery if the fitter had any brains.
Or
Find the relay, unually in/under the boot or one of the boots side panels or perhaps behind a rear light.

Most of the wires will splice into either sides rear lighting wires or maybe piggy back them, but one will be connected to a 12v feed somewhere and should have a fuse inline, again if the fitter had any brains, it should be easy to find, one end or the other!

If the fuse (when you find it) is ok, move on to the earth and make sure there is a good one to the body somewhere (another wire from the relay)

If it's blowing the fuse when getting wet, try applying vaseline to the socket (smear it on to the pins on the socket on the trailer and push it in and out a few times)

 

[Sweetsixteen]

If your car rear light, signals etc still work normally, it is probably as Goudrons said - a dedicated fuse has blown.
There is space behind the rear lights, which are easily removed (two self-tapping screws either side) and there is possibly a fusible link tucked in there.

The remaining question is, why did any fuse blow just because of a downpour?
This needs to be sorted at the same time.

In my lighting socket on my towbar I have packed non-setting mastic, the same as is used for swimming pool low voltage lighting fittings. Jammed in tight after warming the mastic, this is a totally waterproof sealing method.

 

[PuntoHowTo]

The trailer lighting relay will have its own fuse independent of the rear lights which is what godrons is talking about.

Another favourite place for these is an switched ignition feed somewhere around the steering column.

Do take the spare wheel out and make sure you've not got an indoor pond as this can point to water leaking round the back lights or boot seal which needs fixing before putting a new fuse in the system, depending no how the relay is installed it could have ended up submerged

 

[oinklet]

Or
Find the relay, unually in/under the boot or one of the boots side panels or perhaps behind a rear light.

That's where it was, just behind the rear light. Fuse changed and all working fine again.

Thanks to all for the assistance.

 

[A3jeroen]

You mean that whoever installed it put the inline fuse near the relay instead of near the battery?
I'd change that ASAP.

gr J