Stage 8 – Wiring the Electrics

Wiring the Electrics into the bus was one of the most daunting tasks we faced; with neither of us having any previous experience, the whole thing seemed very confusing!

We hope this diagram and steps help make this an easier process for you

  1. Make a diagram of everything you want to wire

This is important. It will enable you to have a clear picture of where every output / power requirement is going to be located in the conversion, what your individual and overall power consumption requirements will be, help you start to consider where cabling might be installed and how many outputs your fuse box will need.

Finding previous examples of wiring diagrams online was quite difficult, as everyone’s requirements and set ups are different, and not so many seemed to include solar. However, as we have no electrical experience whatsoever, after as much research as possible (and hassling friends and the kind folks on ‘Self Build Campervans’ Facebook Group) we put together the following wiring diagram:



Essentially it is quite simple really. The 200W solar panels and the Van’s alternator are the power sources and the 12V appliances and outputs leading from the fusebox (top to bottom on the right – Water pump, Waeco Fridge, Water Heater, Mini Projector) and the 240V sockets wired to the inverter are the power requirements. [In the end we had to wire the gas hob ignition to the 240V Inverter too as the 12V campervan ones seemed unnecessarily expensive so we opted for a standard kitchen sized 4 ring gas hob that was 240V.

  1. Install, wire and earth the Relay Unit

So the first job, before building the electrics board, was to install the Relay Unit. The purpose of this is to allow current from the vehicle’s inverter to flow in one direction towards the power bank. This means when he vehicle is running, the alternator creates electricity and when the starter battery is full it can then start filling up the batteries in the power bank. It then cuts this power off so that you could essentially drain the power batteries but maintain a full starter battery; so in theory you should never have a flat starter battery.


Here is how we wired in our Relay Unit and the Battery Powerbank. The Relay Unit is connected between the positive terminal on the starter battery with 16mm 110A Battery Cable and the positive terminal on one of the leisure batteries in the powerbank. Either side of the Relay we wired in 100A ANL MIDI fuses, and a battery switch so we can cut the power from the starter battery/inverter if need be. [A good point to note here is that you never want to run your batteries to empty as this drastically reduces their life. Try not to use more than 50% or let them go below 12V/12.1V as a rough guide]


To connect the 16mm 110A cable to the relay and batteries you will need to attach the correct sized eyelet terminals to the cable. To do this we trimmed the cable, soldered the ends slightly, inserted them into the ends of the connectors, hammered the ends of the connector with a pin punch several times (to crimp the connectors to the cable) and then added more solder using the blowtorch and some silver solder. After a few attempts we quickly realised you need to slide the shrink wrap black tubing onto the cable first before adding the connectors, so that they can then slide down over the connectors and be shrunk to cover the joints.


Labelling cable ends might be useful here. You also need to earth the Relay. We did this by removing the paint on a section of the chassis and bolting a negative cable to it.


  1. Install 100A MIDI Fuses

Run 16mm Cables to the Leisure battery bank through the cab chassis. On our van there were several holes already made and sealed with black plastic caps that just popped out and were perfect for feeding the cabling through, so it’s worth checking for these before drilling more holes. We also included cables and an isolator switch to bypass relay in case of emergency start, which would link all starter and leisure batteries together.


Then add connectors to the wires and attach the inline MIDI Fuses. We opted for 100A here. Whilst it is incredibly unlikely that the Ampage from the starter battery would ever spike anywhere near this, the cable can take up to 110A and the relay 150A so if this is what you are protecting with the fuses then there is no harm going to 100A safely. I decided to fuse either side of the relay as to protect both relay unit and battery bank. I am not sure if this is completely necessary but made sense for only a few pounds extra to protect the battery bank.

  1. Install the Leisure Battery Bank

The number of Leisure batteries and their Amperage Hours of storage that you include in your battery bank will depend on several factors. One consideration will be whether you are installing solar panels or just running off the alternator alone. Another will be how long you intend to stay stationary in various places. Another will be what applicance and lighting will you be pulling from the battery bank. And finally your budget will affect your choices of battery.

For us, as we are using solar and travelling to relatively sunny places over the summer, we would expect to pull in between 7-14A per hour from the solar alone. We do not have many high Amperage drawing appliances, with really only the inverter powering 240v sockets for laptops and the mini projector. With all these things on, some lights and the bedroom fan on, we probably use around 5-6A per hour. That means that during the day we have more power coming in from the solar than we can really use so it is just a store for cloudy/rainy days and night time. We are also considering adding a 12V fridge to pull some ampage during the day and turn it off at night.



So.. we opted for 200W solar power on the roof to compliment the alternator power source, one 110A heavy duty leisure battery and one 130A heavy duty leisure battery with dual terminals. Some people said that you should use the same size and manufacturer of batteries, and some said that it didn’t matter at all. If building a full scale house leisure battery bank I would, but for the size/cost of our set up I don’t think it will make very much difference. I chose the double terminal battery to be the first and main battery in the bank, with all positive terminals going into this one, and all negative cables onto the smaller one.


The smaller one was positioned behind an existing fuseboard (that had to stay where it was) and the larger one was positioned between the fuseboard and the wall, with a simple timber frame around it to keep it in position. On top of this frame sits the switch/fuse board and the solar controller unit. This means all parts of the set up will be ventilated, out of sight when the counter top and cupboards are installed, accessible from the driver’s seat if necessary in emergency, and I can see the input/output readings on the solar controller unit easily enough from the driver’s seat.

  1. Wire in Switches and Fusebox (add photo completed)

So now is the slightly tricky job of wiring in the cables from your batteries, your isolator switches, fuses for the switches and fusebox. You are aiming here to get the fuses as close to the switches as possible (as recommended by the manufacturer) and use as little cable as possible to reduce cable resistance to current.

  1. Add negative bus bar (add photo completed)

The negative busbar unit essentially collects all the negative cables from your appliances and lighting (anything getting the positive cable wired into the fusebox) and joins these negatives with one 110A cable to the battery bank/other earthed part of your wiring system.

  1. Run 2 core cable to various 12v appliances

Having a drawn plan (would recommend the free program Google SKetchUp here) is incredibly useful when considering how to best utilise space in your conversion, but it also plans a fundamental role in the electrics wiring. Without a pretty clear idea of where every appliance, switch, socket and light will go is imperative before you can start wiring in appliances and lighting cables. With appliances, some of these can be wired in once the plywood skin in added to the walls, but some (especially the lighting if you are having downlights) needs to be wired into the insulation, so you need to know the exact position of each downlight and switch at this very early stage of the build.

  1. Wire in all the lights in a series circuit imbedded into installation

Lay a good quality dual core cable into the insulation. Add insulated connections where necessary and wire in enough cable to drop down inside potential walls so that you can wire in the switches for the various parts of the circuit.


You may have to add plywood skin over insulation at same time as wiring to keep checking the system is working. A few times I had misjudged screwing or nailing the plywood up and then had to remove the whole thing to find where I had punctured the wire with the nail or screw.. verrrrrry annoying to have to take it all down once it is up. I would recommend marking on each plywood sheet exactly where the cables lie underneath it so you do not puncture any wiring below throughout the remainder of the build !



It’s a hell of feeling when you have all the 12V system wired in, the downlights plugged in and you have power and lights on inside… all powered by solar panels on the roof!!


  1. Wire 12 Volt to any fans you are installing into the roof. 


  1. Run 240 volt cable to inverter, and wire in the invertor. Split 240 volt cable with junction boxes and add in plastic socket boxes. 


You may choose to do this now or later once the walls and furniture are installed. I certainly opted away from having any 240V wires in the walls as I wanted to be able to see all wires and connections easily, and this would mainly be at floor level anyway so easily hidden in cupboards, under sofa and in bed storage space. It just seemed like a safer option.

  1. I also decided to wire in a very precise ammeter to the battery bank so that I get very accurate readings of what current I am drawing from the battery bank, so I can see what Watts and Ampage I am currently using, and the exact level of battery Voltage. I originally positioned this in the electronics cupboard because the blue light was fairly bright at night, however, it really is something that you want to be able to see from as many spots in the bus as possible, so it is now wired up through the driver’s seat cover and is positioned in the back of the driver’s headrest. I would absolutely recommend this to anyone if they are using a cheap solar controller (like the ones in the cheap kits like we did as their readings are very inaccurate)

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