Hi, dont know if anyone can advise - we are due to go on our first camping trip soon using a trelgo t40 trailer my husband bought off ebay. Worked fine when it was picked up, but tested it today and the right indicator doesnt work - works fine on car, but nothing on trailer and no beeping sound in car when indicator is on. We've tried replacing the bulbs, and checking all the connections on the bulb assembly and the plug that connects to the tow bar but still no luck.
We had a similar thing, and I tracked it down to the pins in the connector on the trailer and in the socket on the towbar. I used a small screwdriver to "open up" the pins (they are a split design) so they made better contact with the sockets they go into. There should be six pins on the trailer side and 3 on the towbar side. Then give everything a spray of wd40.
Have you dismantled trailer plug & checked connections? If ok then problem could be car socket. You need to check for power at car socket, with indicator flashing put voltage meter across earth pin3 & r/h indicator pin4 to see if you have power. If you have then problem is with trailer.
Just be careful with the WD40 it eats plastic type materials just like the stuff on your plug and socket.
Ok now and again but it will eat away and distort the shape.
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Dual electrics shouldn't be the issue. I always have trouble with the indicators and it is mostly down to the plug and socket not liking each other no matter how much fiddling with the pins and use of contact cleaner. I find that the most important thing is to not force the plug in too hard.
Another thing that it could be is that sometimes the main cable from the plug on the trailer goes to one light, then there are cable joins to the cable that feeds the other light. You can tell if yours are like this if you open both lights and find one has far more cables (or if you can see the back of where the lights are fixed, one has two cables going it to it with one of the cables going to the other).
Also as a continue on from Tentz post, run twelve volts to the two contacts on the trailer plug side. This will prove that you don't have a break on this side of things. It's quite common for either side of the plug or socket connection, to suffer from bad contact where the wires are grub screwed into position
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