How do you build a motorcycle wiring harness from scratch?

Answer 1

Take time and get a good wiring diagram

Get a large ply or chipboard board and some pin type nails

Ideally lay out the old loom onto it , if not possible then measure (TWICE) every wire

The loom should be a bit like a tree with main trunk and branches off leading to individual "twigs"

Get all the wire in all the colours you need BUT first mark out on the board each wire, the colour on the board nail in pins along the length and at each place the branches and smaller twigs come out. Where there are more than one wire put pins in a semicircle and fan the wires out. Also mark the type and size of connector, What each goes to and what it is ( ie flasher relay or ... rear stop lamp then rear light they will have different wires going to the same place)

once you have the "loom" laid out you can lay out the new wires, leave plenty of spare wire ESPECIALLY if you are doing any modifications like new fuse box OR say a relay board as opposed to individual relays all over the place.

You should then have wires laid out branching off to small connections

Once you have checked and double checked you can either use shrink wrap or self amalgamating tape OR the fabric tape or a mix of all 3 and wrap the loom.

If unsure use cable ties to loosely "open" wrap it all which will allow you to move wires if needed

Lay it on the bike make sure all the wires reach where they need to . use shrink wrap for single and small groups only once you are sure everything is where it should be use GOOD crimps and crimp the terminals.

As an aside aircraft looms are made with crimp joints so you DO NOT have to solder.

Always get the correct terminals

Good crimp pliers

good side cutters and wire strippers

Boxes of grommets are available at places like Maplins

it takes time and effort but can be done ..the older the bike the easier it is.

Make sure you ALWAYS use black for earth and do not be scared of earthing all places like rear lights

head lamp and other components it WILL stop the vibrations killing stuff prematurely

I think that is about it, in the UK a complete rewire can cost circa £850

That said the actual wire, terminals, crimping pliers cutters and all the other "stuff" you need is NOT cheap DO NOT SKIMP on cheap terminals or tools you WILL regret it later.