how to ......make a wiring loom

Discussion in 'How To' started by Diddymen, May 14, 2012.

  1. Diddymen

    Diddymen Moderator

    Most of us at some point or another will have been faced with the birds nest of wires behind the dashboard, countless additions and bodges, poor connections and intermittent working of electrical items.

    The busses wiring could be likened to the veins in your body distributing power to where ever it is needed, unfortunatly the bus cant repair minor injuries to its wiring .......and neither it seems can countless PO's !

    So it comes to pass that you are the custodian of 30 years + of bodging, brittle wires and bad connections.

    Vehicle electrics are often over looked or neglected, even in a number of restored vans I've seen. As Im sure your all aware, poor connections can cause a localised build up of heat and overloaded wires combined with bad connections can put an undue strain on things and you have the potential for a fire.

    So there comes a point where it is better to re-wire the whole lot and start again. This is a service that we can offer at Ginger's VW if you are a bit daunted taking this on your self or supply the loom ready made to your specification.

    In this 'how to' I will show you a few tricks of the trade, of building a new vehicle wiring loom

    before starting there are a few things we need to get ready

    Firstly, you need to sit down and think about everything you want to incorporate into your loom

    Do you want a standard loom?, do you want to keep the diagnostic plug? do you want to uprate the cables? do you want to include new or extra circuits such as reverse lights? make a list and take your time to plan it out - the last thing you want is to make a nice loom, fit it then realise you've left something out so you end up having to run loose wires through your bus to fit the fog lights you'd forgotten about.

    I would advise making a seperate loom for leisure electrics, ICE systems to avoid interfearance and certainly dont run 240V hook up wires in the proximity of 12V wiring as this can induce dangerous currents into the 12V system when 'hooked up to the mains' Also making separate looms keeps the size down - remember that small rusty pipe under the bus that it has to fit through?

    then you need to get some wiring diagrams of your bus (top tip - lamminate them if you can) .....or I should say, diagrams of how your bus should have been wired when it left the factory, you need to get the correct diagrams for the year of your bus - is it UK bus USA? etc

    many of which can be found here -

    Once you have got the diagrams it is worth doing a survey of your existing wiring and comparing to the diagrams, taking plenty of notes with regards to wire sizes and colours, any extra circuits which have been added and any modifications which have been done.

    ...........but your still not ready, you need to get a few more things things. This list is not definative, you can use your initative but we now need to get parts to make the jig for your new loom so you will need -

    cup hooks large (approximatly 20)
    cup hooks medium (approximatly 20)
    cup hooks slightly smaller than medium ;D (approximatly 20)

    these are what I mean by cup hooks -

    assorted nails and screws
    note paper
    a big marker pen
    cable lables
    if you need it - a digital camera may come in useful

    we will get to the parts to build your loom once it is pinned up and a jig has been made

    next space, the main loom from end to end is approximatly 710cm long, you will need a large area to pin out your new loom and all the branches.

    Once you have got your work area and sundries ready, and you have surveyed your existing wiring and made notes of any discrepancies, you are ready to strip out your old loom.

    Make sure you lable every wire before disconnecting even if you will be throwing the old wiring away (obviously dissconnect the battery first) you will need the old loom as a pattern to make sure the new loom will line up as it should in all the right places

    Obviously if your going to buy a new loom then a lot of this wont be relavent.

    In the next post (once I have uploaded the pics) I will show you how I pin out the loom
    Last edited: Oct 2, 2017
    salad.dodger2 likes this.
  2. Great post so far, thanks
  3. Im interested in this as I think I might have to this route.great advice.
  4. Diddymen

    Diddymen Moderator

    thanks guys :) updates wont be fast I'm afraid as I'm fitting this in around other jobs

    but heres some work I did earlier ;D

    ok, so hopefully we've got all the bits we need to make our jig and the loom has been removed from the bus so we are ready to pin it up.

    start with the larger size cup hooks and leaving your self some space for the whole loom, screw about 10 of the hooks in line along the top of your board/wall/work area.

    Once you have this first line you can lay your loom along it ( I would start with the cab end first at the top) and tie it to the first hook to stop it slipping onto the floor........unless your doing it on the floor ;D

    next you can form a nice bend and double the loom back on its self and make another row of cup hooks beneith and parallel to the first row.

    once the loom is layed in the second row you can go back and pin up the bend you have just made using more cup hooks - on the outer bends its best to have the hooks facing outwards.

    repeat this process of back and forth gradually using smaller hooks as the loom tapers into narrower points. If you run out of room, go back and move each of the rows up slightly untill you have made enough space.

    and you should be left with a loom hanging nicely on the wall like this


    once you have the main part of the loom up you can use the smaller size hooks to do a similar thing to each of the sub branches of the loom like so



    Once the basic shape has been formed, use a big black marker to draw out the run and start labling points (so when you remove the loom you will know which brach is for what)



    you can then go back through the jig and add extra hooks for support, every so often putting a hook upside down to hold the shape


    the reason for this is, when you run single wires they will behave differently to a nice thick loom all taped together, inverting a few hooks will help to keep the individual wires bundled together before you tape up the loom. You will also need to go back to the bends you made in the main loom and add extra nails to the inner radius - again, this is done to get a nice shape to the individual wires you run.

    Next you need to pull the individual wires comming out of the loom taught to get the length, whilst holding the wires tight put a screw or nail into your jig to mark that length, you need to do this to all the ends of the wires. Take your time to do this as A) you want the right length B) to try and keep it all neat



    I've left the smaller looms and loose wires connected to my loom so I've hung these out of the way for now


    lastly then, you need to pin up your wiring diagram and a bit of paper to make notes


    Next time we will be tracing the wires to see which goes where (it isnt always wired as logical as you'd think ::)) so you need to buzz them out with a tester, check the colours and sizes of the cables, mark on the jig the cable sizes, colours, destinations and start measuring up

    so you will need a tester a bit of string, marker pen and more note paper ;D

    with any luck I'll get that done next week
    Last edited: Oct 2, 2017
    salad.dodger2 likes this.
  5. looking good
    When i use to make them i used a 8' x 4' sheet of ply wood to lay it out on.
    I use to take pictures of the connections still connected and stick this on the board at the right place to help visualise what the ends of the cable did
    Last edited by a moderator: Oct 2, 2017
  6. Don't fancy an all expenses paid trip to Cambridge do you? Lol. I could do with a hand just to reconnect all wires at the front of the bus plus establish what's missing?!
  7. Reading through this great until that last picture of the full wiring diagram. WTF is all that about. My head has just exploded
    salad.dodger2 likes this.
    Last edited by a moderator: Oct 2, 2017
  9. Diddymen

    Diddymen Moderator

    Sorry I've not updated for a while..............theres not been much to update!!. I have started making a list of parts I will need though! and will order the bits soon and start making the new loom

    Last edited: Oct 2, 2017
  10. Diddymen

    Diddymen Moderator

    a little update........

    started putting together a parts list for the wiring loom, I'd already done a bit on the main loom so I started looking at the cab loom


    looks like a mess and a little scarey if you've not tackled it before but its not that bad, I left as much connected to it as possible when I took it out (as I was too lazy to lable it all up) ........make sure you all do it the right way if your unsure and take lots of pics!! make notes and lable everything

    from there I could lay it all out neatly and start measuring, make sure you have lots of room, a pen, paper and some way of measuring the cable sizes - I used a digital vernier)



    as well as noting cable size, colour and length you will also need to count up the size and trype of crimps you will need (I will be using original style non insulated crimps and fitting covers where appropriate.

    its worth noting that some of the original sizes and colours of cables are no longer available (or not easily) so I will be going for the closest substitution and using thin wall cable (not to every ones taste) but it carries more current for the relative size.

    for example - 1.5mm thin wall isnt available which is the size or the original, in some instances I will be using 1mm thin wall instaead as it will still carry more current than the original PVC 1.5mm in other instances such as lighting I will be uprating the cable from 1.5mm to 2mm.

    Once I have compiled the list I will work out what combinations of colours I have not used, and will use these for the 'extras' I will be fitting to aid with identification in the future
    Last edited: Oct 2, 2017
    salad.dodger2 likes this.
  11. Diddymen

    Diddymen Moderator

    once again appologies are in order for the length of time from my last post!! lack of money, lack of time, other jobs on the bus taking presidence and waiting for cables has slowed me down a bit!

    On the note of waiting for cable, certain cables colours are no longer available - some places will manu[glow=red,2,300]FACT[/glow]ure them ....but at a cost! I have had to order 100mtr reels of certain colours I needed as they only make plain colours in 4mm and above. The 3 colour hazzard lights you cant really get manu[glow=red,2,300]FACT[/glow]ured either,....unless you want 5Km....which I'd say is a bit much!

    so far I've probably spent over £350 (or more :eek:) which is more than buying a loom off the shelf, but I have bought some new crimp tools and wires for extras to be fitted into my custom loom, and I should have enough wire to make another loom to recover some of the initial outlay

    but I digress!!!

    hopefully by now you will have made a jig and put together a shopping list

    next then is to start running the wires them selves. In the first post about making a jig, I meantioned putting markings down .....this is where it becomes really important as you will have to take your old loom off of the jig and you will be working from your markings or cryptic they better be good!!

    it is best to work from the furthest points (rear N/S lights) towards the cab end, wrap the first wire (your choice which one to run) around one of the screws in your jig marking where the end of your old wires. Follow the loom structure, running this cable until it gets to its destination and wrap it around the corresponding nail/screw ....and cut the excess wire off so you have a turn of wire around each of the 2 screws.

    by working from the furthest point first you should avoid a lot of crosses in your wires making them untidy....this cant always be helped if you have to wait for wires - you will fit what you have to hand, and then the others once they arrive!

    building up your loom a 'branch' at a time.

    there is no secrets to how to do this (which is why I've not bothered to take pics of this stage), getting it neat will come with practice or taking your time. Just make sure you dont pull your individual cables too tightly following your jig as you will end up with your loom being a little on the short side!....try to make sure you follow your jig but keep the cables a little on the loose side.

    hopefully you should end up with something looking a little like this



    the loom is now neatly layed out but a lot of loose cables.

    you may notice I have added in a few extra cables to my loom which are more noticeable in the next pic where I have an extra branch exiting by the starter cables


    now you have all your cables in place and you are happy, its time to remove it from your jig .....but before you do, use cable ties to bunch the individual wires to each other and to hold the loom together.

    you can now remove your new loom and you should have something like this ;D


    ok, so it looks a mess! but providing you have cable tied it all together neatly you should now be able to untangle it easily and lay it out for the next part


    Last edited: Oct 2, 2017
  12. Diddymen

    Diddymen Moderator

    once it is layed out, start replacing the cable ties with insulation tape (a single wrap of cable is all you need) as the sleeving wont fit over the cable ties!

    I do mine every 5-6 inches, working from the furthest point (rear N/S lights) and working towards the cab, taking out any twists or crosses as I go trying to get the cables to lay as neatly as possible expecially at the 'branches'



    you will undoubtably get a few crosses and 'bunched' up cabling especially if you are doing this bit all on your own.

    to get the tape as tightly as possible it helps to have some one pulling the loom tight for you while you put the tape on.

    Next then, is to sleeve it up, I have been using various sizes of heat shrink

    start at the furthest (and thinnest) part of the loom in the same direction as I started putting the tape on - you will see why in a bit (in other words, put the first bit of sleeving on the end of the N/S rear light cluster wiring)


    first bit of heat shrink is on, I have left this a bit shorter than I need at the 'open' end as I will be adding another bit to hold the earth in place for the rear light - like the original


    the other end should tuck a little way under the next branch will see why in a bit


    next we can start shrinking the tubing down using a heat gun (hair drier might not give enough heat for some tubing!!)


    you can see with a little application of heat that the tubing shrinks down nicely onto the cable loom


    be careful though, the tubing can retain the heat for quite a while so dont burn your selves!

    next I ran the earth wire for the rear lights and sleeved that in - with the sleeving ending at the right place at the 'open' end


    then sleeve the brances next in line that you have tucked the first bit of sleeving under - in this case the number plate light branch. Those of you with keen eyes will notice some extra wires there too. These will be for some engine bay lighting!!

    be sure to sleeve up the branches next in line each time before you start sleeving the main body of the loom


    the reason being is that now you will need to run a new (probably next diameter size) sleeving over the first bit you have shrunk, and the other branches. Slide the sleeving all the way over and then back a little way to hold the branches in place and then shrink down.

    Make sure you measure your sleeving carefully before cutting as it will be a pain to remove it to cut it down - or to replace it with a longer bit of the correct length .....this will become harder the further into the loom you get!

    so you should now have a well supported branch like this with the other end tucked under the next branch

    the other end of which looks like this (the branch here will be going to the old diag position where I will fit the switch/fuse for the engine bay lights)


    then carry on along the loom in the same fashion, each time sliding the sleeving over all the previous bits until it reaches the correct position.

    here I have had to do things a little different for the off side rear light earth, I have the branches going in different directions, so I have had to sleeve the next part of the main loom first


    and then used a short piec of sleeve to support the branches and make it tidy


    I always try to use the minium size sleeving I can get away with and shrink it right down, it does make the loom in these places a bit stiffer to run, but once in place it should hold it shape better, give more support to the cables and so reduce 'chaffing' and the risk of breaks deep in the loom from fatiguge it will also reduce any dirt and oil getting up inside the sleeving, which can happen with the original looms with a 'looser' sleeving

    there will more soon once I have updated my resto thread with the pics, all this info is in my thread but probably spread around a bit so you might have to search for it!! there may be other bits of info in there that I have missed off of this thread, as I have tried to keep this as condensed as possible.

    if you want to check out my resto thread it han be found here:-
    salad.dodger2 likes this.
  13. Epic work.

    Want to make me one :)
    Last edited by a moderator: Oct 2, 2017
  14. Diddymen

    Diddymen Moderator

    give it a go :thumbsup:
  15. Seriously!!!, i'd rather spend the money once getting it made for me than ruining it myself :eek:
    Last edited by a moderator: Oct 2, 2017
  16. Diddymen

    Diddymen Moderator

    Last edited: Oct 2, 2017
  17. This is great. Thank you :thumbsup:
  18. @Diddymen I am considering following your lead on this one.

    Any chance you still have some of the wire lying about I could buy some lengths off you rather than buying rolls.
  19. Diddymen

    Diddymen Moderator

    it would be ok ....for some of the loom but its only 1mm and you will need various other sized wires, the length is only 5mr which wont be long enough for the main loom under the van.

    You can check the sizes of wires on the wiring diagrams for your year of van (see link in first post). Go for the correct colours if you can, but you will find some are not available, or only available on 50mr rolls which is over the top if your only making one loom so you may have to make substitutions.

    I'm currently making up 2 looms for others at present so I don't have any spare wire I'm afraid
    deadturtle likes this.

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