Towbar socket - no power

Duplicate post deleted...

Apologies quad_red. I had a long post providing instructions on checks to make posted and the post duplicated. I went to remove the duplicate post, editing and just putting in a note that it was a duplicate and low and behold it removed both posts. This new version of boards while it may have better functionality in places seems to be horrendous on the whole...bring back the old version. Have to be somewhere else now but will aim to get my reply reposted to your thread before the day is out.

quad_red, apologies my post got deleted earlier.

I would say the first thing to check is that the wiring is intact into the by-pass relay from the towbar socket and from the tail light wiring loom. Assuming it's similar to the way my Avensis is wired this should be housed behind the carpet-cardboard type panelling on the side of the boot. Could be the panel on either side but most likely the passenger side as this is the side of the car the tail-light wiring loom will be coming down the car on. You will likely need to take the threshold over the boot opening off first and there may be a couple of luggage tie down hooks that may need to be taken off to get this off. Then there will likely be plastic poppers you will need to ease out to take that boot side panelling off.

Check that the wires from the towbar socket are attached into the by-pass relay first. The wire will be coming in through the body of the car somewhere. There should be numbers versus colours wrote on the by-pass relay and these wires will likely be screwed into the relay. Just check that they are wired in correctly and the connections are good. On the wires coming from the tail lights to the other side of the by-pass relay they should be spliced into the taillight wires with either scotch locks or butt connectors, crimped and heat shrink over the top if done correctly. Check the connections are good by giving a moderately firm tug on each wire. If the connections are made with the wires wrapped around each other and some insulating tape on top as is often done you might want to make the connections good and proper. Check that both the wiring from the towbar socket and the wiring on the other side are earthed to the body of the car correctly.

Assuming done correctly there should be a permanent live feed from the battery or fuse box to the by pass relay. As I understand this wire should be ran directly from the battery to the by-pass relay. In reality it is likely more often ran from the fuse box. I ran it from an unused but permanent live fuse in the fuse box below the glovebox in my Avensis. It would have being a nightmare to run the wire from the battery through the firewall of the car. I piggybacked off this fuse as such using the correct adaptor. The arrangement on mine is that there is a fuse in this adaptor inside the fusebox and this permanent live wire then is ran back to the by-pass realy - Its branched into two separate wires and each of these wires are in turn fused and they then feed separately into the by-pass relay. These fuses are again visible behind the side carpet-cardboarded area in my case. If you have a multimeter check you are getting between 12 and 13 volts on these wires somewhere you see access. If done correctly these should be permanent live (rather than ignition live) so you should get a reading without the ignition being on. If you are not getting a reading best thing to check first is if the fuses are blown. If they are replace them and recheck.

If not getting a reading then next thing to check would be the other side of the permanent live going into the battery or fuse box as mentioned will most likely often be the case. Check if fused there and if the fuse is blown. If your happy your connection and fuse are good but getting no reading from the permanent live at the back of the car then you are likely checking your permanent live wire is good along the run of the car and not broken somewhere - pulling off door sill covers, bottom of the B pillar panel on the inside of the car...anything else that is covering the wire along its run.

The above checks are based on the assumption that your towbar is wired in broadly in a similar manner to my own but there can likely be a few variations of how the job is done.

Was providing my directions on the assumption that the lights in the trailer were known to be good but absolutely, it would be the first obvious check to make if not already verified.

I know now as I seen it happening since. Issue was I didn't know at the time. Deleted what I assumed to be one of the posts that duplicated for whatever reason and low and behold it deleted the whole lot never to be seen again.