HONDA CB750 FOUR PART 7 – construction continues with the first part of the wiring.

1. Work on the Honda CB750 cafe racer project continues

From day one of this cafe racer project I have always had it in my mind that all wiring should be well and truly hidden. To many really good creative bikes are made with little or no thought for the wiring. I like my wiring tidy and when ever possible hidden. When you decide to build the bike you have always wanted, or a bike you think that manufactures should have made, some elements of the build will always be compromised by budget, the shear practically of the idea or the simple fact it would take to long to make.

Too many people are fearful of wiring and hence it is usually one of those areas of a bike that gets neglected. If you are prepared to spend a little time and effort a neat and tidy custom loom can be made. The basic equipment for making your own loom is an assortment of different coloured wires, a soldering iron, solder, heat shrink, electrical tape, and a few connectors.

‘Vehicle Wiring Products’ have a good range of various electrical supplies and can be found on the web. To save money, if you can find a scrap car, you can remove its wiring harness and recycle it. Ideally new cars that have been written off, so their harnesses are quite new. This will give you a variety of colours and the harness will be longer than a bikes, so giving you plenty for adjustment. Wire where the copper core has gone black and tarnished should not be used. It will be hard to solder and will be more prone to failure.

Connectors are really not that important, as you can solder all wiring without using them. The advantage of no connections is that there are no breaks in the wire and the potential for corroding connectors is avoided. The disadvantage is that if you have to remove a part it will need to be cut off and re-soldered back on. I have built bikes in the past with no connectors and aimed to keep all wires as intact as possible. There is good sound reasoning for this. Any break or connection in a wire creates resistance and the accumulative effect of this is voltage drop. For example, if you have a poor headlight output; you change the lens, the bulb and think the application of a fully charged new battery would cure it.  You failed take into account the half a dozen old connections between the battery and the bulb. It might have been more cost effective to replace the wire between the two with new wire with less breaks.

Manufactures of motorcycles tend to have plenty of connections and redundant wires. The reason being is that they have to sell their bike in many different countries and so need to add extra or different parts to the same model of bike. If you construct your own loom you can eliminate these unnecessary wires and simplify others. The routing of the cable can be improved too as they are often placed for ease of manufacture. There is nothing worse that seeing a load of cable ties on a frame tube. It smacks of poor design and lack of thought, hence wiring should be of equal importance to that flash end can you got for your exhaust system. In the planning stage of custom bike building it is one of those thing often overlooked.

2. Front exit for the wiring loom near the ignition box.

For my bike the wiring will be as simple as possible and run where ever practical in the frame tubes. I planned the route of the wiring in advance when I was modifying the frame. The main harness will run up the main tube under the tank and exit near the ‘Boyer’ ignition box.

3. The finished wiring for the 'Boyer' and coils. Tidiness is next to Godliness

I decided not to use the con-volute tubing for the harness in the end as shown in photo 2. I heat shrank the whole lot and used the plastic braided harness cover for the length from the head stock to the headlight. One of our stainless steel clips was then used to hold the harness in position. The whole resulting wiring is neat and tidy with the minimum of connections ( photo 3. )

4. The alternator wires are run in a length of braided hose

The wiring from the alternator was a bit of a problem but was solved by the use of some braided hose to make a feature of it. A piece of aluminium tube and a stainless ‘P’ clip were used to secure the bottom of the hose covering the wires.

5. Rear Brembo master cylinder - the stop light wires run in the frame tube.

The rear brake light switch is fed by a wire running down the rear diagonal down tube and exits near the ‘Goodridge’ brake light switch. It is one of the bits of visible wiring, so I covered it with a rubber boot.

Switch gear is keep to a minimum, with the lights wired on permanently, so only a high/low beam switch is required. The other switch required is the engine cut switch and horn button. In the next part I will show you how the rear is wired, the switch gear wire is fitted and how the headlight is arranged.

By Colin Jones