Electricity flowing through a cable is a bit like water flowing through a hosepipe. If someone kinks the pipe, the water coming out the other end slows to a trickle.
Over time, cables and especially their connectors develop the equivalent of hosepipe kinks. Corrosion, butchery, cheap connectors and physical damage to wires all make it harder for electricity to flow. This leads to dim lights, cooked rectifiers, poor starting and so on. When high resistances start building up in several places at once, you need a new loom.
Yes. If any faulty workmanship on the loom crops up within three months I’ll put it right free of charge. Fortunately it is in the nature of wiring that if it works properly it’ll keep working properly for a good long while. Before you pick your bike up I will demonstrate the complete operation of the electrical system. My guarantee doesn’t include other electrical components dying, such as regulator rectifiers, bulbs, alternators, batteries and so on.
This is a big subject. I wrote an article about it in 2017 on the Bikesocial website. They’ve chopped it into bite-sized chunks. The main things to choose are battery, regulator rectifier, indicators, switchgear, lights (front and back) and speedo. You will also be wanting a fuse box, flasher unit and starter solenoid, but I didn’t include them in the article.
Some people are drawn to the Motogadget M-Unit system, which allows you to programme in various tricks such as connecting your bike to your phone, or varying your indicator flash rate. Motogadget also claim that their M-Unit simplifies your bike’s wiring (it doesn’t). An M-Unit is basically a box that takes the battery power and distributes it to the various bits of your bike that flash, beep and spark. A bit like humble wires, you might say. My advice: these things cost a lot of money, and require a constant battery drain, so before you buy one, ask yourself the question: what problem will my custom bike have which an M-Unit will solve? If you can answer the question convincingly, go ahead. Otherwise, save your money.
This is a nerdy question because nearly everyone leaves it up to me. But here are the pros and cons of different systems.
The cheapest and most compact multi-connector is the Miniblock. It was original equipment on most Japanese bikes in the 1970s, 80s and early 90s, and can easily last decades. Advantages: quick to assemble, packs a lot of wires into a small space. Disadvantages: moderately awkward to pull the blocks apart, slightly open to the elements where the wires go in. Molex connectors, used on some 1970s Italian bikes, have similar virtues and failings.
Sealed connectors, such as the Superseal ones used on 1990s Ducatis, or the Sumitomo, Delphi or MT plugs on many late 1980s onwards Japanese bikes, have little seals to offer near total weatherproofing. Superseal blocks are a bit iffy in my experience. The Japanese sealed plugs, while more expensive, are a better product. The downside with sealed plugs is that they are fiddly and therefore a bit more time consuming to assemble.
Deutsch are the Rolls Royce of connector block manufacturers, and their prices reflect that. The weatherproofing is superb, they’re reusable, they’re quick and reliable to assemble, and separating the blocks is a piece of cake. Most block sizes can be clipped to a flat surface too. The one big snag is bulk: Deutsch need a bit more space than other kinds of connector block, and there isn’t always room. The biggest virtue of the Deutsch system is its super-slim pins. These allow you to make re-usable joins with no connector blocks at all – just pins hidden by heat shrink. It’s almost invisible, which is handy on a custom bike.
Most original equipment loom builds use several types of connector, depending on exposure to the weather, current flow and which component they’re attached to. But they always favour one main type, and it can be any of the above.
A quick word on Japanese bullet connectors, which are the standard for one-to-one or one-to-two joins. They are quick to make up and space efficient. Annoyingly their insulators are designed for fatter old-school cable, rather than the thinwall cable available today, so the looser fit makes them very slightly open to the elements. They can also be tricky to prise apart. Nevertheless, they’re indispensable. Not to be confused with Lucas brass bullets, which belong in the past.
This is about how you want the main trunk and branches of the loom to be bundled up. Simplest and fastest (and therefore cheapest) is a spiral wrap with loom tape – the main parts of many original looms are protected in this way.
Smaller numbers of cables can also be threaded through vinyl sleeving (another original equipment technique). Vinyl makes it easier to trace wires (and therefore faults) around the bike, because you can see the colour of the cables disappearing into junctions and connector blocks. All the same, that shouldn’t be a concern of ours.
You can get black braided heat-shrink sleeving in a few sizes. It looks great on British bikes, but needs a little care because the ends must be sealed with glue-lined heat shrink or they fray.
Racing or custom bikes often have a polyolefin heat shrink outer cover on the bigger sections, or even on all the sections. You build it up like a tree in reverse – twigs first, then branches, then the main trunk, sealing with overlapping heat shrink each time. This is my favourite system. It’s tricky to make but looks good and is hard wearing.
Yes. As long as they aren’t badly corroded you can remove rust and renew connections to make them perform like new. On all my looms I run earth cables back to the main frame, rather than trust to the current finding its way back through mudguards and headlight brackets. This helps preserve good performance for a long time to come.
I also rebuild any new pattern headlights, tail lights and indicators. They are often made hastily, with connections that could fail quite quickly – especially tail lights. It’s daft not to make them as good as they can be.
Yes – but it’s not the best idea, because it creates problems later on when you fit something that fouls a cable or wotnot. Wherever possible it’s best to work on a clean, fully finished and painted bike – with all the electrical parts securely mounted. I can make battery boxes and mount regulator rectifiers if you want, but it’s not the best use of my time – or your money! If you need a direct replacement for a standard loom, it helps to have the standard loom in place. And for the bike to be properly clean.
A very common problem when I try firing a bike up after a loom build is blocked or leaking carbs. I have to start the engine to test charging and ignition. If the bike’s preparation makes this impossible, I have to fix it. This can take a long time and add a large amount to your bill (we’ll discuss it first). Amal carbs are the worst offenders: the alloy is extremely prone to wear and corrosion. My advice is: be realistic. It’s a lot cheaper to buy new carbs than try and make worn-out ones work.
Another frequent issue is painting the frame before thinking about where the electrical components (fuses, reg rec, flasher unit, ignition box etc) need to go. My advice is: find a secure, properly-mounted home for ALL your electrical items before you proceed to the powder coating stage.
Fruit cake every time.
Sometimes it’s a couple of months, sometimes a few days. Ring or email for the latest.
After all, what could possibly go wrong?
Well, it’s a bit like chess. You have to think several steps ahead.
Let’s assume you are happy making electrical circuits, you understand parallel and series connections, and you can choose the right gauge cable for high and low current parts of the loom (Vehicle Wiring Products and Kojaycat have helpful advice on their sites). Unless you are a genius you will then require a full colour wiring diagram to work from. You need to visualise how it will lay out around the bike in the most invisible and durable way. As that is a 3D problem, a 2D wiring diagram can only get you so far. This is the hardest part. As for materials: for a reasonably complicated loom, around £200 of crimp tools, wires, sleeves, tape, solder and connectors might be enough.
The main thing after that is to make smooth splices (the point where cables split into two or three). You can do this with solder or crimps, but if there are any sharp edges they can work their way through the heat shrink and cause a fire. I use little files to smooth every splice. You also need to keep the splices (which tend to stiffen the bundle of wires) away from places where the loom bends. Old Brit and Italian bikes don’t have any splices. Instead, they make all their double and triple connections externally, where the weather can get at them. It’s a bit of a mess but it makes for a much simpler build. And it works – at least when the bike is new.
On the other hand if you’re baffled by electricity, never read instructions and frequently walk into glass doors, you might be wise to give loom building a miss.
Assuming the cables aren’t eaten by rats, or submerged in seawater, or repeatedly drenched in fuel and oil, it will last a very long time. I’ve seen old Honda looms, built with exactly the same construction techniques, still working nicely after 20 or 30 years.
Easy one, this.
1. Fit worn-out or bunged-up carbs so that the bike is impossible to start once the loom is built. (I have to start it to test the charging system.)
2. Get it painted before you have found a home for all the electrical accessories. (You can’t build a loom until they’re all screwed in place!)
3. Insist on push-button switchgear with through-the-bars wiring, a Motogadget M Button and a bluetooth M Unit. It takes hours to fit, costs a fortune, and does… the same as a normal setup.
A custom motorcycle wiring loom diagram takes three to six hours to design, depending on complexity, so £75-£150. You can have it as a PDF or an A3 colour print. You can see examples for most of the bikes in the Recent Jobs section.
Fuel injection needs a lot more cabling of various sizes, and lots of different connectors to plug into the various sensors. Hand-building a loom like that gets very expensive – maybe £1500 or more. But hey, I’ll do it!