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Discomikey's Custom Series III wiring harness design


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Hi all,

Its come to the point where my wiring harness really needs replacing, its a mess, and its age makes its safety a concern for me. A few months back i drew up a wiring diagram including the entire standard series layout, but highly altered to include a bank of relay's and a proper fusebox.

I have decided to locate the fusebox and relay bank inside the lower dashboard at the drivers end, and modify this to be released using quarter turn fasteners.

I was looking online for fuse holders which are configurable etc and couldnt find much for cheap that will do the job, but i have remembered that i had my old 200TDi disco fuse holder still, its short by 6 fuse slots but i should be able to find another 10 bank one to compensate and leave extra blank slots for future use.

I have modelled a small section of the bulkhead where i will fit the fusebox and relay bank so i can design the layout previous to actually starting the harness. I also have a spare bulkhead which will act as a mockup bulkhead. This means ill get the harness pretty much complete apart from end terminations before it even sees the truck.

First question: IIRC there is someone on this forum who can supply electrical connectors etc from the standard LR range? I need to make a few purchases from him!

Second question: If i add up all the amperage requirements of the ignition switched circuits it seems to require a massively large feed wire and fuse, relay etc. so to benchmark, does anyone know the +ACC current rating of the range rover P38 or discovery 2? i.e. if theres a fuse for the whole lot? i could use this to benchmark.

Third Question: i'm after a veriety of different sized IP67 crimp style multi pin connectors, these MUST be of the bulkhead type

Thats all for now. Ill use this thread to follow the design and build of the harness.

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Watching with interest!!

Kettle's going to be getting a full new harness when she gets her new chassis. The existing wiring is very poor now, there's an ordinary exterior junction box on the rear chassis leg where the looms failed and be reconnected! I think I'm going to drive up to Autosparks with her on a Friday, so they can have a good look at her and tell me what I need to order off the shelf to suit her, rather than trying to do it by phone or email, or trying to pick the right bits off the website. I don't know if there's anything they've got to suit the TDi or if I'll be redoing that again myself.

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Vehicle Wiring Products have basically all you need.

Vehicle building solutions do very nice stuff..

I've build several looms for various vehicles - biggest one was a 4x4 DAF Truck with living and a waterbed - but never anywhere near "original". My 110 has over 60 fuses, 20 relays and a few non standard options for security. Serious amounts of cable went in and a custom build computer database to document it all. There are just numbers - no colour codes. The Series Hybris has a loom build by me and that has lasted over 20 years of abuse.

Use the best quality cable, connectors etc. you can afford, take your time building and document what you do.

Have Fun.

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Watching with interest!!

Kettle's going to be getting a full new harness when she gets her new chassis. The existing wiring is very poor now, there's an ordinary exterior junction box on the rear chassis leg where the looms failed and be reconnected! I think I'm going to drive up to Autosparks with her on a Friday, so they can have a good look at her and tell me what I need to order off the shelf to suit her, rather than trying to do it by phone or email, or trying to pick the right bits off the website. I don't know if there's anything they've got to suit the TDi or if I'll be redoing that again myself.

autosparks do harnesses for a series with a TDi engine conversion :)

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Vehicle Wiring Products have basically all you need.

Vehicle building solutions do very nice stuff..

I've build several looms for various vehicles - biggest one was a 4x4 DAF Truck with living and a waterbed - but never anywhere near "original". My 110 has over 60 fuses, 20 relays and a few non standard options for security. Serious amounts of cable went in and a custom build computer database to document it all. There are just numbers - no colour codes. The Series Hybris has a loom build by me and that has lasted over 20 years of abuse.

Use the best quality cable, connectors etc. you can afford, take your time building and document what you do.

Have Fun.

I use VWP a lot, i like to use decent quality stuff too. I've found a couple of busbars suitable for the application and have designed my fuse/busbar/relay layout. Ordered the busbars and relay holders, ill send the bracket off for lazer cutting as soon as i get the other parts (to check measurements against the CAD data i have found/made)

in the images below, blue = bulkhead, Purple = fusebox, black = relays, red = permanent live busbar, brown = +ACC live busbar, orange = local harness routing

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I shall try and keep a spreadsheet of all the costs and components used, we'll then see how it costs out against something from autosparks or the likes

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That's accounting for spots, dip, main beam, heated screen/mirrors etc and a couple spare slots for the future. I need to add a glow plug relay (hoping I can use one of those holders) and a timer relay for the heaters.

The flasher unit will be mounted seperately somewhere nearby

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I needed to redo all my wiring as it was nearly all wrecked. I did consider the autosparks route, but couldn't justify the price so I made my own.

The wiring has 7 core trailer cabling to the lights, and in the engine bay.

The original loom behind the dash is still intact, as it was pretty much ok. The supply comes from a new supply feed, through a 60amp relay, with associated switches every wires is fused, then there is a relay for the clocks and all feeds, a realy for the coil, fuel pump, and starter.

That feeds the standard wiring, now instead of going to say the lights, I used the as triggers for relays, so the lights actually work, these are again all fused.

Looks a mess, but this was during installation and is now all nice and tidy.

I HATE wiring, and is totally DIY.

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Update time:

I have ordered everything i should need to make a start on the lighting harness. I've also created a costing spreadsheet so we can see how much it totals to.

The initial parts orders arrived:

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This includes 2x busbar, 100x fuseboard terminals, some wires for going from the busbars to the fusebox and relays etc, and the relay holders arrived.

Still to arrive are the lighitng harness wires, along with the econoseal connectors for later style sidelights, proper headlight bulb connectors and some double contact relays for the headlights.

I fabricated the fuseboard bracket:

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Here's the wiring diagram i created to help me spec everything@

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and the connector layout diagram to help me spec multiplugs etc

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and the location of the fusebox:

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I've been de-pinning the fusebox and the first 5 or 6 terminals came out really easy, the rest however have put up a real fight! still not finished yet.

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Parts have arrived and the first few circuits almost complete (lighting harness)

fusebox and relay board are being populated as i go along and each "set" of wires destined for a different location have been seperated out and temporarily taped together at a rough length to be cut down when fitted.

not much in the way of pretty pictures yet though!

I have ordered the bulkhead connectors today at an overall cost of £56. not cheap but will make the harness so much smarter and more serviceable. my original plan was to mount them to a plate replacing the grommet plate where the harness normally comes through. although unfortunately these connectors aren't quite compact enough to get more than two in each side without modification. i could get 3 in at a push with some grinding:

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However, as i have a scrap twisted bulkhead. i can nick the pressed opening panels from that and use them to extend the original hole on my bulkhead. like so:

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meaning i can get 4 bulkhead plugs in the drivers side, and still get 2 in the passengers side.

a couple more angles so you get where im heading:

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I use VWP for most of my bits. I kept it simple on my rebuild - I repaired the original loom, which wasn't bad, removing all previous mods and returning it to standard except for the engine wiring, which had a few variations in lengths for the connections to the Tdi. I only added a reverse light system to the loom and cut short the head light feeds to control relays mounted on the inner wing, one for dipped and one for high beam and spots.

I spliced indicator side repeaters into the front indicator wiring, as these use low wattage bulbs and are within the standard looms capacity, and added an LED red strip to the rear door glass as a high level brake light.

The Tdi glow plug relay was wired up independently of the loom, the only connections to the original wiring being the output of the relay to the cold start warning lamp holder, a trigger and kill wire off the ignition switch terminals and a connection to the battery.

The accessories, including stereo, rear screen wash wipe and all screen, mirror and seat heaters (and even the heater blower fan) and engine cooling electric fan all run from a bus bar from a second battery (split charge relay), all using 20A Carling Tech switches to avoid the need for relays, simplifying the circuits and saving space.

The original loom retains the fuse box under the steering column (even post PAS installation), though all the fuses are now used and the order was changed a little to be more appropriate. The accessory loom uses a Defender fuse box below the dash.

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  • 4 weeks later...

I've been ordering components section at a time. I have the fusebox and relay board set on a scrap bulkhead, all of the lighting parts of the harness are poplulated into the fuse and relay board. and have been laid out in their respective "run groups" with plenty of excess wire. At this point i measured for the multiplugs and cut through each group of wires at the point they go through the bulkhead, then populated the multiplugs as necessary.

I have just tonight ordered the majority of the rest of the components required. all the wires for the engine and cab harness. with the exception of some of the dash harnesses and bits im not 100% sure about yet.

The new plates to replace the grommet plates in the top of the bulkhead have been designed and sent off for laser cutting from 2mm stainless. the multiplugs will mount to these and poke through.

There are no more pictures as of yet as it doesnt look like much. i will take a photo when obvious progress has been made. Current spend tally is around £275. still under what a standard complete harness would be without modifications.

I'll be happy if it stays under £400 all in. Remember, i'm doing this properly, not cheaply.

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