Friday, 8 June 2018

Range Rover P38 - Adding extra circuits

In the past, I’ve successfully (and easily) added circuits to Range Rover Classics without any real issues, however, we’re now dealing with a ’38….a whole different set of challenges.

On a Classic, during its development over the years of production, extra circuits were added by Land Rover in a rather haphazard manner, so we ended up with relays in multiple locations, fuses in multiple locations, and a wiring loom more complex than a heap of spaghetti.

The scenario is much neater in the ’38 – there are two fundamental fuse boxes, one in the engine bay and one under the drivers’ seat (the venerable BeCM) and all the relays are in the engine bay, in the associated fuse box – tracing things and replacing things is far easier – you don’t even need to remove trim.
With this in mind, I wanted to avoid the miss-mash of circuitry found in the Classic when adding circuits to the ’38.
I am proposing to add….


  • Winch switching circuits (one front, one rear)
  • Light bar circuit (probably 4 lights running as 2 pairs)
  • Beacon circuits (for recovery operations during off road marshalling duties)
  • Wiring for a Viair pump, acting as a 2nd EAS pump (to cope with the enormous Arnott Gen 3 bags)
  • Various circuitry to isolate the battery split charge system from the 2 winches


As with the split charge project, first problem is space – again finding spaces for circuit components involved stripping the interior until a big enough void was found.

The passenger seat came out, and underneath there seemed to be a large enough hole to fit in all the relays and fuses I reckoned I’d need for the project.
Here’s the available space….



….not generous, but workable I hoped.
There’s already a relay there (the timer relay for the EAS) – ignore the green relay to the left of the picture, this is a remnant of a previous mod and will come out during this project.
I was after as much future proofing as possible, so the aim was to fit a larger fuse box than initially required, and more relay bases than initially needed – hopefully this would ensure no re-work in the event on further additional circuits in the future.
I made 2 brackets up – one fits to the grp frame that contains all the ECU’s, and one is bolted to the seat base upright
Here’s the semi-finished set up in situ….



On the rear plate, I’ve mounted the relay bases as low as possible, as some of the relays fitted are not standard, and are taller than a normal switching unit - the big yellow relay on the left is a Land Rover voltage sensitive switch (PRC4427) which I’ve utilised to control the split charge system for the 2nd battery, and the tall black relay (centre left) is the TRW timer relay for the EAS, more or less in the same position as it originally was, but re-wired to a new relay base. Finally, we have 3 relays for the beacons and light bar.

On the front plate, I’ve mounted a fuse box (Land Rover Defender, also the same as a late 80’s Range Rover Classic) and the relay for the 2nd EAS pump. The 3 empty relay slots are for the future if needed. These relays sit higher (to clear the fuse box) but will still be removable with the seat in position.

On the far right of the front plate is the main input power source for the relays, which comes direct from the battery in the engine bay. This is fused in the battery box, splits, and feeds directly into the fuse box to step down the fusing for each individual circuit.
Both plates are 3mm aluminium, and are not painted, replicating the ali plates Land Rover use to support the ECUs nearby.

The switching circuits are fed from the cigarette lighter feed (fused in the original car loom at 30A) which now has a solder joint, splitting the single feed into multiples, which are then individually fused via the fuse box. I’ve tried to keep the fuse box layout so it makes some kind of sense, so fuses are in pairs for each circuit. The ‘box is laid out like this….



Here’s the wiring schematic I’ve used to create the circuits – the big vertical line denotes the bulkhead…



Note the beacon and CB radio circuit is direct from the battery so I can run them with the key out, everything else requires ignition on, just to make sure we don’t deplete the battery too much.
The seat base trim has also been adjusted – now it has a rectangular cut out in it, and a clip-on cover – removing the lid gives access to the fuses – it’s a direct replica of the drivers’ side, where a panel gives access to the BeCM fusebox. The fuse box legend above is stuck to the inside of the access cover, meaning I don’t have to try and remember what I’ve done down the line if a fuse blows!



All the wiring has been bound with loom tape, and the switch loom runs under the carpet insulation, up the side of the gearbox tunnel to emerge in front of the gear selector in the ash tray void.
I’ve disposed of the ashtray and the cigarette lighter aiming to use the space for Carling Contura II switches. In addition to the switches, there is also a double USB charge socket, so the loss of the lighter does not impact my ability to use a satnav or charge my phone. Here’s the fitted switches….



The switches also pick up the illumination circuit (from the lighter wiring) so they will light up when the side lights are on, meaning I can find them in the dark.
Unfortunately, I’ve filled this void, so any future switches will have to go somewhere else in the dash – we’ll deal with that problem when it arises, for now, I have enough!

The wiring that runs to the front passes through the bulkhead in the passenger foot well, and I’ve fitted a connection point just inside the engine bay, that way if any damage happens to the loom in the engine bay, I can carry out repairs without having to undo all the loom in the passenger cabin.

Fortunately, Land Rover have left a blanking plug in the bulkhead for the bonnet release cables on a left hand drive car – popping this blank out, and fitting a grommet instead allows cables through into the engine bay without the need for drilling – the loom emerges just under the fuel evaporation canister, adjacent to the existing loom, keeping everything nice and neat.

As you may have noticed from the schematic, I couldn’t put all the fuses in the seat base – in some instances it was important to ensure the fuse was as close to the battery as possible (to reduce the length of un-protected circuitry) Adding to the original under-bonnet fuse box was not possible, so a new sub fuse box was created in the battery compartment – it contains the primary fuses for the power distribution (MAXI fuse) and the protection for the split charge circuit (see different blog) – here’s the fuse box…



It sits under the battery box lid, so remains out of the way and protected.
There are no doubt many different ways of adding circuits, but I’m quite pleased with this project – it was a lot of work, but has ended up reasonably neat I think, future proof, and safe.

No comments:

Post a Comment