Trailer Rebuild: Designing An Electrical System

Trailer Rebuild: Designing An Electrical System

If you are new to this camper trailer rebuild; click HERE to head back to the first post and see what you’ve missed.

So now that the chassis is finished, it’s time to start thinking about the electrical installation. As I have mentioned in a previous post, we are scrapping the 240V installation; and that’s for two reasons. The first and most notable reason is that we just don’t use 240V any more. It’s pretty rare that we’ll sit in a caravan park, preferring to be out in the bush or a national park campground. The second reason is that we can avoid paying a sparky a fortune to come and wire it all up!


So we all got to thinking about what you need in an electrical system, which is surprisingly difficult due to the sheer number of gadgets available these days! Some must have’s were:

  • LED lighting, inside and out
  • A 240V inverter, just enough to charge batteries really
  • USB outlets for charging phones, cigarette sockets for other 12v appliances
  • Electric pump for the sink and a tap on the drawbar
  • Power for the 50 litre Waeco which will have a home in the trailer
  • DC to DC smart battery charger, fed by vehicle and solar input
  • Power for the cooktop which has an automatic igniter

And then there were some other things which crossed minds but were quickly dismissed, such as:

  • 12V stereo system, we can just use an Ipod dock or something
  • Larger inverter for running big appliances, we’d never use it to it’s capacity
  • Some sort of hot water system. But we don’t have the space, it’s another expense and we have a kettle
  • LED strips in the bed ends, not entirely necessary.

So here’s a plan I came up with. Bringing back memories of high school technical drawing class, I grabbed some grid paper and started doodling. The drawing below shows the interior layout as a birds eye view with the components in their proposed location. I’ve uploaded these in larger detail than normal too, so click the image if you’d like to see it in EXTREME CLOSE UP!


The drawbar is at the lower end of the image, and if you were wondering what “coiled cable to roof” is for, it’s to run power to the interior and exterior lights, and to bring power down from the roof mounted solar panel.

Now there’s the drawing showing mounting positions for lights and solar panels on the inside and outside of the roof:



The kitchen in this trailer has to fold over to allow it to close. The sink and stove are located in the top half, and the bottom half will house the brains of the electrical system on one side, and storage on the other. The diagram below shows a rough placement of the equipment:


And last of all is the bit that took me aaaages! It’s the diagram linking everything up. I’ve got a bit of a clue when it comes to 12v electrical, but I’m no auto sparky. I pulled together something that is hopefully overkill at worst; with the help of Redarc’s Cable Size Calculator


You might notice I’ve left a regulator for the solar panel out. Whoops, it will go in though. And I know it’s possible to get a Redarc BCDC with solar input and regulator built in, but I’ve already got the older model on hand meaning I’ve gotta figure my own system to make it switch! The tail lights and marker lights have been left out of this diagram, they are easy enough to do and I’ll be running them in a separate loom anyway.

So what do you think? What would you add to this system? Is there anything you’d do differently? That’s the thing about electrical systems, there are a billion and one ways of doing things and it all depends on your tastes and your needs!

See you in the comments I suppose!

Camper Rebuild Part 4 is now up! CLICK HERE to have a look


Alex Garner


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  1. Chris
    July 24, 14:29 Reply
    Awesome looking stuff Alex. I've just finished re-wiring my camper trailer from plug to taillight a. Thankfully before any accessories went in (it's a brand new trailer but I wasn't happy with the "quality" of the wiring). Admittedly, no fancy drawings for mine, just slid underneath the trailer for a couple hours and now it's bush proof. Next up is the battery system and lights/sockets!
    • Alex Garner
      July 24, 20:18 Reply
      Ah, they didn't quite think you'd push the trailer to it's full potential hey? It's a good feeling when you've done something yourself and you know it'll be rock solid for years to come. And if it ever does go wrong, you were the one that did it so you're more likely to know where to look for problems :)
  2. Will
    July 24, 15:01 Reply
    Hi Alex What is the BCDC? You could connect the twin core 6B+S (from what looks like an anderson plug at the front of the van) direct to the battery, assuming its coming from the tow vehicle and therefore 12v, then you wouldn't need the input change over as (if as I suspect) the BCDC is a voltage regulator. When the battery is being charged from the tow vehicle the regulator will sense a voltage input and won't connect the solar panel to the battery. When the input from the tow vehicle is disconnected the then regulator will sense this and allow voltage to flow from the solar panel to the battery. Also keep the cabling from the regulator to the battery as short as possible as this is regulated voltage and therefore more susceptible to voltage drops. I have a similar idea in my L300 4X4 to charge an auxiliary battery and so far works a treat. Used a Morningstar regulator (no affiliation, just did a fair bit of research and without spending silly money that one came out on top) Love your website by the way.....loads of good local useful info Will
    • Alex Garner
      July 24, 20:14 Reply
      Hi Will, The BCDC is a multi stage battery charger from Redarc that charges directly from 12v rather than 240V. They are recommended to get the most out of AGM or Gel batteries in particular and prevent issues with voltage drop over the long cable run from the front of the vehicle to the trailer. Likewise, I have no affiliation with Redarc, we had the BCDC destined for the previous trailer but it never ended up going in before we sold it. As it is an older model, they didn't support power from multiple sources (IE, vehicle alternator and solar panel). So I need to set up a relay which will send power from the solar panel when not connected to the vehicle, and switch to power from the anderson plug when that is plugged in. The latest BCDC's support multi inputs straight out of the box. I have looked into that morningstar regulator I think and at a glance they seem pretty good value for money! I'm interested in the L300 4x4 you have too, those things are pretty capable and make a great platform for a camping rig! Glad you love the website too mate :) Alex
      • Will
        July 27, 08:24 Reply
        Hi Alex Yeah the BCDC makes way more sense now, as you would have a fair voltage drop from the tow vehicle to the van battery. My L300 4X4 is a pretty good camping platform. I have custom built a bed/drawer/storage system in the back and so far it's ok. I will email you some pictures.....its not too pretty but it works!!! Cheers Will
  3. James
    July 24, 17:41 Reply
    Great wiring diagram. BCDC is the way to go for sure, nothing looks after an AGM battery better than a good DC-DC charger. Your solar will need to have it's own regulator as the BCDC1220 doesn't do solar.. not a big drama really. Wire in a 'changeover relay' between the BCDC "output to battery", and the solar output, the "trigger" will be a single wire feed from a spare pin on your trailer harness, I think pin2 is 'reverse lights' (which campers don't usually have), or you could use the brakes pin if your trailer is unbraked. Now, loop a wire from your Patrol anderson positive (at the back of the patrol) in to that pin 2 of your patrol trailer harness, it provides a solid 12V from the starter battery all the time, no matter what, consider it a trigger wire. Your changeover relay will get that 12v feed from that pin at all times if it is plugged in to the car via the trailer harness. When the trailer is NOT plugged in to the tow vehicle, the 12v feed on that pin is obviously disconnected, the change over relay will 'cutover' to solar. You just need to ensure your config on the relay is right. if relay gets 12v trigger, use BCDC, if relay gets no 12v trigger, use solar. I can show you more. I just did exactly the same thing. This will save you pissing around with any extra manual switches too. bonza.
    • Alex Garner
      July 24, 20:03 Reply
      Cheers for the info James! Yeah in John's last trailer there was no BCDC on the battery and it never got a full charge, cos of the voltage drop I guess? BCDC should fix that right up :) I follow you with the changeover relay and the unused reverse light wire in the trailer harness, that's a good idea and should fit in very nicely! Yeah manual switches are to be avoided wherever possible. It's not because they are unreliable, it's because the human behind the switching is :p
  4. Telf
    July 28, 07:03 Reply
    Good to see the progress but just one comment on the solar side. I have had a similar set-up when we lived in Perth with the solar panel permanently mounted on the roof. Its a catch 22 because while convenient, you generally park the camper in the shade on purpose or the only place you can park dictates that you are in shade. The solar panel then becomes a total waste of time as the sun doesn't hit it. I now use a folding panel on my new camper and have made up a few 5m 6mm leads with Anderson plugs so I can place the panels anywhere and only use the minimum length needed. That way I get the camper in the shade (or wherever the campsite dictates) and can place the panels where needed in the sun. Other than that, you've got an awesome build happening.
    • Alex Garner
      August 01, 20:34 Reply
      I certainly see what you mean there mate! Folding solar was considered, but there are a few unique reasons behind our choice of fixed panel. 1: The camper is likely to be towed by a few family members, who's vehicles don't have anderson connections to charge it. This way it can get some charge from the sun. 2: The fibreglass roof is sagged a little, the mounting framework for the panel will be designed to also help keep the roof from sagging As a result, we have really gone overboard with the panel size. I originally purchased a 200W panel, but it was a little too large. Now it's got 150W up there, with room for expansion if need be (solar is so bloody cheap these days!) I'll probably have a play around with all sorts of setups, a wind turbine would be pretty cool! I'm a bit of a tinkerer :D
  5. marcus
    August 03, 06:32 Reply
    Hi Alex, great job. My wife and I are rebuilding exactly the same camper right now. How can I get in touch with you please?
    • Alex Garner
      August 04, 22:00 Reply
      Hi Marcus, send me an email if you like.
  6. […] and I guess it kind of has been! Last time we visited the camper trailer I was planning the electrical system. And the time before that we had just completed the chassis build. Well now the body is on, and we […]
  7. […] no worries there. Before fitting new veneer panels, I looked back on the wiring diagram I made in THIS BLOG POST and ran wiring behind the Meranti frame to make my life easier. At this point, we also fitted new […]
  8. Snowflake
    June 10, 07:06 Reply
    Excellent effort fellas. Really enjoy following your progress on the rebuild of this camper trailer.

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