A while ago I upgraded the lights on our caravan by changing the functions round and added two new LED reversing lights which I can’t understand why I hadn’t done this years ago. In daylight they are bright… and at night they are really bright… retina burning bright according to reports. Reversing into a dark pitch is a lot easier and safety wise having an additional set of tail and brake lights with two large bright rear fog lights instead of the single factory 21 watt light mounted almost as low as you can get on the rear of the caravan is a vast improvement in my mind. You can read about my changes here… “Put Yer Lights On Mate…“

Following that article I had lots of people contact me letting me know they liked what I had done and considering upgrading themselves. Not a clue if anyone did, but that’s how these things go. I did have another email from a gentleman which was a bit different. Now I’ve edited it a bit as it was originally two emails and included a company name and some specific details which I’m sure they would not wish me to publish to the world…. here’s the gist of it though:

“Hi Simon, been reading your blog for a while and I read your post about upgrading your caravan lights. I was wondering if you might be able to help with something we would like to do with our trailers or could put us in touch with someone who can? We have around eight trailers that are used on various locations separately or as a group and are towed by a variety of vehicles, mostly our own but occasionally by contractors. Most of our trailers have additional side lighting powered off the trailers own batteries which are charged from the vehicle or while on site from generators. A lot of our set up and tear down is done at night and we have had issues at dark locations where the vehicles reversing lights don’t really help. Is there any way we could get the side work lighting to come on when the vehicle reverses but could be controlled from the vehicle without any additional switches or alterations to the vehicles but could be turned on and off as reversing on a public road with them on might not be legal”

From an exchange of emails, I do know what the company does and some of the sorts of places it works. They don’t always have access to mains power when setting up or tearing down and would like something that can easily be installed in a trailer without too much alteration to the electrical services. Nothing could be installed in any of the tow vehicles as the vehicles were not always their own and I first suggested a cheap(ish) remote switch that could be used by the driver to turn them on and off as required. I was told this was not an option as the remote switches would likely get lost/damaged or need batteries or be with the wrong crew, some sites they could not use any radio equipment.

Time to put my thinking cat on…

I had a bit of an idea forming. Something I’d seen on a Class A American RV (Prevost I think) was a set of spotlights set in the side panel of the RV pointing backwards and located near the front wheel. These lit up down the side of the RV and the ground to the side when reversing…. I’d thought about adding a couple of simple cheap LED lights to the underside of the caravan between the wheel and front of the caravan angled outwards by about 60 degrees mounted under the floor… so when I reversed they lit up the caravan wheel and the ground it was going over so I could see it clearly at night in my mirrors. I had pondered how to switch this on and off using the Amarok but not add any more wiring between the caravan and vehicle. So I’d already come up with a solution.

Here is what I came up with…

It’s a simple two relay set up. The two triggers for this to work are the vehicle reversing lights and the rear fog lights. The top relay in the box is activated by the vehicle being in reverse with the reversing lights on. The lower relay is activated by turning the vehicles rear fog lights on. Only when these two conditions are met, is there a circuit across the two relays switches made thus activating the work lights on the trailer.

Quite simply when reversing to turn on the work light simply turn on the rear fog lights and the work lights will come on.

Cables 1, 2 & 3 connect to the road lights. Cables 4 & 5 are for the switched load. The cost was around £15 for the components for each unit and that included Bosch relays & sockets, the die-cast box and fuse holder. I guess putting it in a plastic case and using cheaper eBay sourced relays could halve that cost.

I did also think that as an upgrade or option the relay operated by the reversing lights could be a timer relay. Set it to say 15 seconds, then when reversing you turn on the work lights and they will remain on of 15 seconds after reversing as long as the rear fog lights are on. This would give you time to reverse, pull forward and reverse again. Each time you select reverse the timer would reset and as soon as you disengaged reverse the timer would start its countdown again.

It was as simple as I could get it using existing signals from the vehicle that already pass through to the trailer. I guess it could be used to turn anything on using any combination of lights operating from the vehicle.

The wiring between the road lights and work lights is kept separate as I wasn’t 100% sure how the trailers power system worked and how it was connected to the road lights (if at all) The two relays were installed in a die cast box with a grommet for the 5 cables. All the trailers were fitted with one of these and apparently they have all been working fine for several months.

Why did I opt for reversing lights and fog lights?

I wanted something that would not be used generally through the day so reversing on a public road during daylight or even at night the work lights would not illuminate. Running during the day with lights on and your fog lights will not operate the working lights… and if you are running in weather that requires headlights and rear fog light… then I guess having the working lights come on while you reverse in those inclement weather conditions just makes you more visible to everyone around. So apart from that I don’t think that you will cause a danger on the road with this set-up.

So…. I think I might just have to install one of these on my caravan…. just in case!

Its a fairly simple DIY job to build a box and install it without too much messing about with the original wiring. Now someone asked me about getting the orange side marker lights to flash in time with the indicators…. and remain as side markers when the indicators weren’t being used. Is this something I need to put my thinking cat on for? Let me know in the comments.