Is it time to replace your trailer lights?
  |  First Published: December 2014

All trailers need to have working lights fitted to them to be legal on the road, but a we all know that one day your lights will be working and the next they’re not. Trying the line, “They were working when I left home, Officer” is usually responded to with, “Sure they were” as you are handed a fine.

Trailer light problems

Even though the police may not believe you, I do. Being an AUVIS (Authorised Unregistered Vehicle Inspection Station) examiner, I regularly have customers bringing in their trailers for inspection only to find that when we test the lights they will have an indicator or side light out. Now the mechanic who wants to earn a quick buck will tell you that your light needs to be replaced and sometimes this will be the case, but before you agree to that, here are a few things to try to get that light working.

Check your trailer plug

The biggest culprit when it comes to lights not working is your trailer plug, especially on a boat trailer. There are a number of things that can go wrong with your trailer plug including corrosion on the pins, pins closing up and not making contact with the cars plug and wires braking off in the plug. Before you pull the plug apart, wiggle it inside the cars plug and see if the lights that weren’t working are coming on when you move the plug. If they are, then it is time to open up the plug and see what the problem is.

Check your earth supply

Before I start on what a bad earth is, I should explain what earth is.

‘Earth’ is a separate wire that runs from the lights to the trailer plug that helps stop them from shorting out. Just like anything that requires power to operate, you need to have an earth. Every light on your trailer will have a power source and an earth. Have you ever been behind a vehicle with its indicator on and the brakes are flashing? This is an example of bad earth. The indicator is trying to get an earth source from somewhere so it is tapping into the brake lights power source causing them to flicker with the indicator. Earth can either be provided through a wire to the lights or from the metal frame of the trailer, the problem with the latter is if corrosion builds between the frame and the light, then the earth connection will be lost.

Check your globes

For all those boat trailer owners who have a globed light assembly on your trailer, it is quite common for your lights to stop working. Your globes can blow, the globe holder connections inside the light can corrode or the wires going into the light can corrode and break off. As soon as you remove the light lens, you will know straight away if it is a simple fix, or if you require a new light.

Broken wires

To check for a broken wire, it can be tricky and time consuming if you don’t have the right tool and that tool is a test light. A test light can indicate if you have power and earth running to your lights. You can pick one up from any tool shop for around $30. Most boat trailers will have the wiring running inside the trailer frame, test the wire and the closest point before it goes into the frame and then again where it comes out of the frame. This will tell you if you have a broken wire inside the frame or not. If you have broken wires it is time to rewire your trailer.

If these checks have been made and the light STILL doesn’t work, then it is time to replace the light.


There are a number of trailer lights available to purchase from all parts of the world. On a boat trailer your will either have globe lights or L.E.D. lights. The type of lights you choose will depend on the vehicle you use to tow your trailer. Most trailer owners don’t realise that if you tow your trailer with a European make vehicle, you will have issues with the trailer lights if they are L.E.D. There are ways around it but that is another article and conversation all together.

When changing the lights on your trailer, it is also an idea to replace the wiring as well. Why? When dealing with boat trailers you are always dunking the rear of your trailer in and out of the water and over time the wiring corrodes and gets brittle. If you just replace the lights, they may still work but if you are trying to solder the wires together they will not bind. Joiners are an easy solution to use if you are only replacing the lights, as they will still make a good connection. If you want to make your lights and wiring fully submersible, then you will want to look at a pre-wired L.E.D. light kit. These kits have the wires connected to a circuit board on the back of the light and then coated with a hardened gel-like substance so water cannot seep into the connections. The wire is then long enough to feed through to the front of the trailer to a trailer plug, so unless you are submersing the rear of your car into the water there is no way water can get into the wiring and lights.

L.E.D. lights

L.E.D. lights are really the way to go when it comes to trailer lighting because they are maintenance free, brighter, look better, fully submersible and easily installed.

Make sure that if you are purchasing L.E.D. lights they state that they are ‘submersible’ and not just ‘water resistant’. Water-resistant stands up to rain but not being submersed in water. This is a common mistake when buying L.E.D. lights and as you can imagine the water resistant L.E.D. lights don’t last long on a boat trailer.

Submersible globe lights

My views on globe lights may not be the same as yours and that’s OK. I believe that if a lens can be removed from a light to replace a globe then it cannot be fully submersible, because there is always the possibility of water getting in. If you are using or replacing your lights with globe lights, I would recommend fitting ones that require a festoon globe instead of a bayonet globe (refer to the pictures to see the difference).

Light boards

Light boards are designed to be used as an emergency system only. You can have a light board permanently fitted to a trailer but you must comply with the following:

• It must be supported at intervals of not more than 600mm along its length.

• It must be insulated at joints.

• It must be located in such a position that it can neither become overheated nor in contact with moving parts.

• It must be protected from chafing.

• It must have a separate earth return wire between the trailer and its hauling vehicle. It is not acceptable to use the trailer coupling or a safety chain or cable as an earth.

Christian Bold, also known as ‘The Trailer Guy’, is one of Australia’s leading trailer and caravan repair specialists. As the Director of Bold Trailers he is a licensed motor mechanic, auto electrician and automotive body builder. Christian is also an AUVIS and e-safety examiner for the RMS. You can contact Christian and the team at Bold Trailers for any information regarding trailer and caravan repairs, maintenance, modifications, legal requirements, imported trailers, parts and accessories and new and used trailers for sale. Their friendly technicians are always willing to help you to make your towing experience safe and enjoyable. For more great tips go to www.boldtrailers.com.au or Phone: (02) 8544 8114.

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