Fuse and Relay Box

For the sake of simplicity I decided to install a new dedicated fuse and relay box to serve any additional electrical equipment I added to the vehicle. This would enable me to take one main power feed from the battery and easily provide appropriate fusing and switching for new equipment without having to disturb or adapt the main vehicle wiring. The only exception to this is where an accessory may be switched via a relay with the switching feed taken from an existing system.

I purchased a modular fuse and relay box from Vehicle Wiring Products and mounted this on the flat inner wing in the engine bay behind the battery (but see revision below). This has space for eight standard 30 amp relays and 16 standard sized blade fuses. The top is protected by a series of splash proof lids whilst the underside is open to allow for all the wiring connections. One side of the fuse holder array is connected together by a bus to which I’ve soldered a heavy gauge wire from the battery positive terminal. Eventually this will be fed from a second battery which will enable all of the accessories to be operated independently without risking the main starting battery.

In the picture you can see the fuse box mounted on the right hand side inner wing. The thick green wire at the bottom is the main feed from the battery whilst the bundle of grey, blue, green and black wires that disappear through the bulkhead are control and switching feeds. The bundle of black wires leaving the top of the picture are power supplies to the roof mounted lights and sockets.

Although I’ve added quite a number of electrical accessories, the fuse box is not yet full, leaving spare capacity for future projects.

Electrical Accessories

Most of the accessories I’ve fitted are lighting, for one purpose or another, mounted on the roof rack. However, I’ve also fitted an auxiliary twin ‘cigarette lighter’ socket on the center console for powering equipment such as phone chargers or GPS and a pair of Hella sockets on the rear of the roof rack for general use. Eventually I will fit another Hella socket inside the rear load area for occasional use of a fridge but this will have to be done in conjunction with a second battery because of the large power drain.

Split charge system

The need for a dedicated split charge system became apparent after buying the Desert Wolf trailer. This has two 100amp gel batteries on board which could conceivably be very flat if we camp in one location for more than 4 or 5 days. The split charger needed to be able to cope with this potentially large load and so a friend of mine built me a purpose-made unit based around a 180 amp relay.

Essentially, this comprises a small low current changeover relay that is used to trigger the main relay via a feed from the  dashboard charge light and thereby connect the vehicle charging system to the trailer batteries. This way, the connection is only made after the vehicle is started and the alternator is charging. The actual connection is by heavy gauge wire, which runs along the chassis inside flexible conduit to the 12S socket on the tow bar.

The two relays are mounted in a waterproof box fixed to the inside of the right hand wing using two existing threaded holes. There are two LED’s on the top of the box, which indicate both that the system is switched on, and that power is being fed to the 12S socket. These indicators are duplicated on the dashboard along with a button to manually switch off the system. The whole system is protected by a maxi-blade 70amp fuse and, depending on the combination of LED’s lit, it is easy to trace whether a fault is due to a failed relay or just a blown fuse.

The manual override is useful if starting in very cold weather as it can be ensured that the main vehicle battery has had some time to recover from that very demanding operation before placing the additional load of two more batteries on the system.  

The picture on the right shows a group of auxiliary switches mounted in a frame to the left of the heater controls. The bottom right hand switch is the manual override for the split charge system and the red and green LED's indicate the system status. Green indicates that the system is switched on and red indicates that power is being transmitted from the battery to the outlet on the tow bar, essentially confirming that the relay has been triggered and the main fuse hasn't blown.

 The three switches on the top row operate the various lights and external sockets on the roof rack.

The switches, and the frame that carries them, are from the parts list of the late model Ranger Rover Classic, which trialed the dash board architecture that would be used in the 300 series Discovery from late '94 onwards. They occupy the space usually taken by a coin tray. The switch frame part no. is AWR1159LNF and there are various switches depending on what you want them to do e.g. interior light, rear heated windscreen, etc. The ones I've used are:

AMR3597 - front fog lights (x3)

AMR3600 - interior light

AMR3605 - blanking plates (x2)

Installation Alterations

To accommodate the installation of a Webasto Pre-heater, it was necessary to relocate the auxiliary fuse box and split charge system. The former was moved to be  mounted vertically on the inner wing, alongside the brake master cylinder, and the latter in the space between the battery and the side of the radiator. This meant that access to these units is slightly more difficult, but otherwise has made for a neater installation.