Making a full wiring loom from scratch

[Viperz888]

I had the great idea to tear out the bodge-tastic wiring from my project mk2 Escort, in the hopes that 'it would be easy enough' and 'there'll be a guide online'.

Unfortunately, it turns out it's harder than I thought to make a diagram showing me how to organise my new loom.
I don't have a problem with making it; its the designing that I'm struggling with. Fortunately its an older, simple car with very little in the way of amenities.
Its planned to be a road going track car, so there is only the bare minimum requirement for electricals.

Even so, I have questions such as what size of wire do I need for which circuits, where and how the fuses should be grouped.

Has anybody done this before, and can they share any tips?

[stevieturbo]

It's a hugely open ended question with many variables, so you need to decide how you want things laid out for your car.

Nobody else can tell you that.

Wire sizes needed will depend on load on each circuit...again, you need to determine that from the parts you intend to use.

For parts there are various sellers that may help with wire, connectors, fuse/relay boxes etc etc

A couple are these.

https://www.carbuildersolutions.com/uk/fuses-and-f...

http://www.vehicle-wiring-products.eu/

[Penelope Stoppedit]

I can go through the whole job with you, unfortunately due to so many time-wasters posting to PH I need to know that you are serious about this and not going to be wasting my time
Send me an email to xxxxxxxxxxxxxxxxx and post here that you have sent that email, I will then go through the whole job with you and very likely post all the information here.
Your Escort is very uncomplicated

Edited by Penelope Stopit on Sunday 3rd March 16:14

[AW111]

I have made a loom from scratch for a 70s motorbike, but there's not a lot to that.
A good friend of mine does wiring for rally cars, including looms from scratch - you only need a couple of wire sizes, but lots of colours.

One thing to remember is to make the loom in sections, eg cabin, engine bay, etc.

But I'd go with Penelope's offer.

[CrutyRammers]

Brilliant offer from Penelope there
All I'll say is, it looks daunting, but when you break it down into individual circuits it's quite simple. If you colour code everything it helps a great deal. The hardest bit I think is working out the load on each wire.

[anonymous-user]

i'd say buy a s/h wiring loom from a car (ebay, scrap yard etc) and take it apart and work out how it's made! That will tell you how it should be done quicker than trying to learn every single hard lesson!

[AW111]

With the classic rally cars I'm involved in, we use circuit breakers rather than fuses for high current stuff like lights. These are mounted on a panel under the bonnet next to the relays they power.

Fuses are usually one or two sets of blade fuses on the dash panel / console / nav panel.

I would make sure you consider aux. power - one car I know now has 3 usb power adapters wired in for phone / camera charging.

[Viperz888]

Penelope Stoppedit said:

I can go through the whole job with you, unfortunately due to so many time-wasters posting to PH I need to know that you are serious about this and not going to be wasting my time
Send me an email to [e-mail] and post here that you have sent that email, I will then go through the whole job with you and very likely post all the information here.
Your Escort is very uncomplicated

Thank you very much - I have sent you an email to the address above.

Thanks also to the rest of you for your tips and insight.

[Penelope Stoppedit]

OK I have mailed you

[Fastpedeller]

IIRC the Escort had bulkhead connectors, which will be difficult to replicate with modern parts.

[stevesingo]

CrutyRammers said:

Brilliant offer from Penelope there
All I'll say is, it looks daunting, but when you break it down into individual circuits it's quite simple. If you colour code everything it helps a great deal. The hardest bit I think is working out the load on each wire.

I'm colour perception deficient, i.e colour blind.

Even I managed to build an engine management loom! Plan it first (Use excel for pins and visio for a circuit diagram) one circuit at a time. It is all in the planning.

[anonymous-user]

stevesingo said:

CrutyRammers said:

Brilliant offer from Penelope there
All I'll say is, it looks daunting, but when you break it down into individual circuits it's quite simple. If you colour code everything it helps a great deal. The hardest bit I think is working out the load on each wire.

I'm colour perception deficient, i.e colour blind.

Even I managed to build an engine management loom! Plan it first (Use excel for pins and visio for a circuit diagram) one circuit at a time. It is all in the planning.

Buying lots of different colours and lots of different gauge wire is expensive,e specially if you are planning on using a high specification wire (ie Raychem etc) Most looms these days are one colour (white) and use some form of specific labelling system to identify individual wires. This means you can just buy a 25m or 50m roll of a few common gauges of the same colour.

[CrutyRammers]

Max_Torque said:

Buying lots of different colours and lots of different gauge wire is expensive,e specially if you are planning on using a high specification wire (ie Raychem etc) Most looms these days are one colour (white) and use some form of specific labelling system to identify individual wires. This means you can just buy a 25m or 50m roll of a few common gauges of the same colour.

Yeah, but it's a pig to debug for the home mechanic. Having fallen foul of "I've got loads of this colour left, I'll use it for this bit", and then had to spend ages tracing wires, I'll pay the extra next time.
You're right though, it can get expensive.

[PositronicRay]

CrutyRammers said:

Max_Torque said:

Buying lots of different colours and lots of different gauge wire is expensive,e specially if you are planning on using a high specification wire (ie Raychem etc) Most looms these days are one colour (white) and use some form of specific labelling system to identify individual wires. This means you can just buy a 25m or 50m roll of a few common gauges of the same colour.

Yeah, but it's a pig to debug for the home mechanic. Having fallen foul of "I've got loads of this colour left, I'll use it for this bit", and then had to spend ages tracing wires, I'll pay the extra next time.
You're right though, it can get expensive.

I had an engine loom made by a pro, it used this single colour method. On a simpler bike loom I made myself I just used blue, as long as you work methodically it's ok

[AW111]

PositronicRay said:

I had an engine loom made by a pro, it used this single colour method. On a simpler bike loom I made myself I just used blue, as long as you work methodically it's ok

A couple of years ago the new electrical guy was given the job of extending the dash harness of a modern diesel for a power pack we were building.

Only after slicing through the inch - thick wiring bundle did he realise there were more wires than colours

[Stiggolas]

I made the loom on my Kit car (Mkll Escort base). As above do one circuit at a time and label everything. I bought a random loom from an autojumble and laid everything out on the kit's chassis. Iran out of wire and used trailer 7 core for everything backwards from the gear lever as I figured it's basically a trailer behind the engine

[anonymous-user]

Stiggolas said:

Iran out of wire

wow, who though PH would be such a hot bed of critical political and strategic News?? ;-)

[anonymous-user]

CrutyRammers said:

Yeah, but it's a pig to debug for the home mechanic. Having fallen foul of "I've got loads of this colour left, I'll use it for this bit", and then had to spend ages tracing wires, I'll pay the extra next time.
You're right though, it can get expensive.

Not if you buy a suitable identification system. ie



The fact you can then label every wire, and cross ref /document it makes fault finding easier imo!


A "loom board" type approach also makes things much, much neater!




use some cheap wire taped together to work out the lengths, routed and junctions, then fix it to a large MDF board. (you can screw cable tie saddles to each node point, with a large cable tie though each one, meaning wires can be slipped into the assy easily, cut to length, labelled, wrapped and then have their end plugs fitted etc

[SantaBarbara]

In a manufactured OEM loom there are different gauge wire for different current and also colour coded strands.

[GreenV8S]

I haven't rewired the whole car but I've built my own engine loom a couple of times and replaced the fuse/relay panel. It was pretty straight forward. The dashboard loom is probably the only significant other complexity you'll face. The approach I used was to lay out the loom in situ to figure out the routing and cable lengths, then tape it up temporarily and take it off the car to loom it. The hardest part was sourcing the right connectors for odd components. I used colour coded wiring and I think that makes sense - I've worked on monochrome wiring and it is a pita. The only thing I'll do differently next time is label both ends of each wire as I make up the loom. I didn't have a suitable label printer at the time and in hindsight I should have got one for the job.