Scoop adapts a 1967 loom to fit a 1970 bike – yup, he’s repurposing a wiring loom.
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Scoop looms large once more!
When I inspected the wiring loom for Project Yamaha CS3C, it was painfully apparent that it was B.E.R. (Beyond Economical Repair).
Far too much had been butchered, overheated, bodged and generally screwed around with. Yes, ultimately most things are rebuildable, but at a cost in both financial and time senses. For reasons I still don’t understand or comprehend, I’d found a loom for a CS1S in one of my spares boxes and to this day I honestly don’t know where it came from.
Looking at the two looms, it was apparent there was a lot of commonality between them, which posed the interesting question: Could I adapt the earlier loom to fit the later bike? In reality it’s not as mad as it sounds and the more you look at these things the more you realise there’s a lot of synergy between the wiring systems of many old Japanese bikes. Of course, a Honda loom isn’t going to work on a Kawasaki without a lot t of pain, but stick to the one marque and things, potentially, can be made to fit. For example, a lot of Suzuki looms run a similar central core with peripheral changes to rear light connections etc., so there’s every possibility that a GT250 loom could be adapted to fit, say, a later T250 Hustler.
Obviously if your bike has an electric start, but your spare loom is a kicker only y then you’ll be saddling yourself with extra work but, with the exception of skiing through revolving doors, most things are, ultimately, possible! What follows is a pictorial resumé of how the process worked out.
I’m frankly surprised how quick this job was. Yes, the two bikes are similar, but not identical and there were several alterations I’ve not included here as they’re all essentially similar to the green/yellow brake light adaptation. New connectors, insulating sleeves, the appropriate crimping tool, sleeving and tape all make the job simpler and faster; they also confer a much greater level of faith in your repurposed loom.
If you find yourself adding an electric start circuit then you’ll need to take into account the heavier wire gauges needed. Whilst you have the loom apart, it’s really worth considering adding an extra earth cable of two from areas that traditionally rely on metal-to-metal contact for the electricity’s return path. Rear lights mounted on mudguards can suffer from poor earthing, and why anyone would seriously expect greased head bearings to earth back to the frame is anyone’s guess. With a bit of planning and some forethought you can save yourself a fair slice of cash and revive an old loom if you go about the process slowly and methodically.
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1/ First task is to reassure yourself that the two looms are reasonably closely related. Here I’m checking the various spurs are similar and marking them with coloured tape to confirm they’ve been checked.
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2/ On the later loom there are three wires, which is one more than the earlier type. The difference is flagged up with a different coloured tape for investigation later. 3/ The brown leads are the live power to the coils; the grey and orange go from the coil to the points. The configuration of the two looms differs slightly, but everything does the same job. If any wires need extending it’s not a major issue at this stage of the exercise. 4/ A wiring diagram from an owner’s handbook has been scanned and enlarged for referencing and checking. If you have access to a coloured version instead of a black and white one it becomes a whole lot easier. Waggle the terminations to check for damaged joints; here the blue wire has failed spectacularly. 5/ Don’t hold back from evicting old insulation tape: it is best carefully removed with scissors rather than a knife, which could easily nick the cables. Brake cleaner on a rag normally takes off the old adhesive. 6/ Yes, I know it’s sad, but I wanted to keep the ID tag from the loom I’m reworking. It will get spliced in later on. 5 3 6
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7/ When you remove old cable sleeving or tape you’ll need to keep the wiring beneath tidy and in the correct place; small, cheap and cheerful cable ties from the Pound Shop are ideal here. 8/ Remember that extra green/yellow wire? It runs to the front brake light switch that was never fitted to the earlier bike. I’ve trimmed some of the insulation from a new length of suitable cable and soldered it inside some thin brass tube from B&Q. The ridged tube then allows me to pull the new section of wiring from the centre of the loom and up to the terminals that all meet in the headlight bowl.
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9/ I’ll sort out the terminations at both ends later, but for now I leave the green/yellow wire uncut in case I need to make adjustments later on. 10/ If you look carefully, most Japanese looms use the minimum of PSA (Pressure Sensitive Adhesive) insulation tape. You might find it used for short runs such as rear brake light switch lines, but that’s about its biggest usage. Japanese bikes normally use sleeving and/or non-binding PVC tape; it’s only the ends that are taped in place, thereby allowing the individual wires to move if necessary. 11/ The CS1C ran an ignition switch terminated with a block connector, whereas the CS3C used individual bullets. Rather than smash the connector block, I’ve winkled out the wires and their brass terminals ready to be modified. 12/ Extra wires are needed so I’ve spliced some over-length sections in place and used solder to secure everything. Some lengths of heat shrink will be slid over the joints and carefully warmed to ensure a decent fit.