Trailer Lights: Running Lights OK; No Hazards or Directionals

I use conductive grease on electrical fittings and ground wire connections to prevent corrosion....You seem to have a bad connection someplace....Easy fix just clean all the connections, solder where possible, and use conductive grease on the rest...check wire continuity, also could be broken wire....

https://www.mgchemicals.com/products/greases-and-lubricants/conductive-greases/carbon-conductive-grease-846

Thanks! I will clean all the connections, it is a good starting point.

I'd probably just buy a complete new light set-up and be done with it.

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This was my instinct too. But I'm trying to be lean considering the project list is long and the season is just a month away!

There's lean, and there's safe.

You beat me to it! When more than one lamp fail at the same time, there's a good chance the problem is a ground problem.

Indeed. A lot of problems can be credited to poor grounding, especially in vehicles that use a frame grounding system. I've had the same issue with older pickup trucks.

Going to be looking at this ASAP. Thank you very much.

Don't forget brake lights!

You mentioned a 4 pin connector. I suspect that means no earth wire. In Oz the standard is now 7 pin connectors. New European cars come with a large 7 pin connector so i would expect that you should be able to get aftermarket 7 pin sockets and plugs. One other possibility is that your vehicle has canbus and it isn't configured for the extra load of the trailer indicators. BUT as you said they worked for a while i strongly suspect a poor/intermitant earth return. This can be tested by using a length of wire that connects to an earth point on the vehicle and the earth terminal in the light set. My experience is that the trailer frame is a bad earth, the trailer to car connection is a bad earth and even the towbar to car connection can be a bad earth. Far better to run 5 or 7 core cable to both connectors. Giving a wired connection from battery terminal to trailer light sets. Mandatory here. Jim

1. Brake light / directional left

2. brake light / directional right

3. tail-marker lights

4. return - ground

you need a steering diode kit if your tow vehicle has separate directional lamps from brake lamps, otherwise directional circuit blinks rear brake lamp in direction of turn

I forgot the U.S. can use brake lights as indicators. The indicators MUST be orange in OZ and all U.S. imports need to modified to comply with Aus. Design Rules. So,,, if there is a separate earth wire i would ensure that the trailer wire comes from the light fitting to the plug And then from the socket to the battery. i.e. NOT either chassis.

I agree with Jimrat. Just forget the trying to fix the wiring which by the pictures was carried out by the Dodgy Brothers. Just get an approved aftermarket sealed LED light kit or buy the lights as individuals.

Wire the whole trailer in new wire and use a 7 pin plug soldering the joins before connecting them in the plug. The plug and socket in OZ have a wiring schedule with each to make life easier.

Trailer lights can be a pain, actually any vehicle lighting can be a pain especially if they are used around salt water or even the fact you guys salt your roads.

It will only take an afternoon to rewire such a small trailer and make the corresponding socket connections on the tow vehicle but remember to seal the back end of plug and socket for salty water or even contaminated water and DC can do all types of etching and electroplating which you don't want.

Having working lights on the trailer saves the embarrassment of trying to remove the boat and trailer from the windscreen of the following vehicle, which is not an approved parking maneuver.

Whenever I've had trailer lights doing strange things, it has been caused by a bad ground.

After 40 years in the trailer boat marine industry I can, with 99% assurance, tell you to check the ground circuit. Trailer lights are almost always grounded through the frame. You 'll see the white ground wire from the light goes to the mounting bolt. Up at the trailer tongue the white wire from the 4 pin connector goes to a bolt on the frame. Who knows where in the various pieces of the frame that are bolted together you are losing your electrical ground continuity. Quickest fix is to run a ground from the 4 pin connector directly back to the lights rather than trying to find the elusive frame fault.

"Quickest fix is to run a ground from the 4 pin connector directly back to the lights rather than trying to find the elusive frame fault."

Also going to be looking at this! Many thanks.

I was in the hitch and towing industry for some time. GROUND IS CRITICAL find a good clean spot on both trailer and tow vehicle add ground like jumper cables and see if lights work. Most good hitch dealers have a test box for truck socket some even have self powered to test trailers. You can use a battery to test trailer independent of truck this helps in diagnosis. You can use test light on male prongs on truck to see if they are all functional. Again GROUND IS CRITICAL.