The big ‘jump’ from the (not so) trusty 6-volt electrics to the better 12-volt system came along from around the mid-1960s through to the early 1970s.
Both the big Brit bikes of the time and the emerging Jap machines pretty much made the switch at the same time but it was a gradual change and some smaller-capacity, utilitarian machines/commuter bikes/scooters and trial bikes were still 6V, although – notably – the Japanese with machines such as the Yamaha RD200, Suzuki GT185 and the like did go 12V.
So what was the main reason to go 12V? For the larger-capacity Japanese bikes the reason was simple: electric start. The amount of current delivered by a 12V battery could do the job, but with a 6V system you’d need a much larger battery! The other reason for the switch was outright performance: you could get twice the lighting output for the same amount of current.
So is there any difference? Well, put simply a 6V, 30 Watt headlamp bulb requires 5 amps to make it work, while the 12V 30W bulb takes half of the amps to do the same job but you’ll get the same level of illumination off of both. Logically, you would say that 12V systems must be twice as good as 6V, but this isn’t always the case as if the generator and charging system can’t support the 12V system then it its better sticking to 6V but keeping that system in tip-top condition. Think of it like a multi-cylinder bike – when all four cylinders are working on a FireBlade – it’s a beast! But if two aren’t, then you may as well have a 500cc parallel twin instead…
In the classic world then, it’s probably best to stick to what you’ve got, rather than swop-out a 6V system for a 12V one: the onus is on originality, after all and (of course) making the best of what you’ve got, so check those connectors and the wiring itself.
Remember, these older bikes were probably expected to last only around 10 years at best – so if you’re looking at a 30-year-old (or more) GSX-R, you’d expect to see knackered connectors and probably a butchered wiring loom. And when it comes to looms on modern classic 1990s bikes, half a decade back it probably wasn’t worth sorting a new wiring loom for it, as it was more than the bike was worth… not so today with prices heading upwards.
Speaking to experts in the field, they say that Honda wiring looms from the 1970s and 80s were top-notch for the time. Fast forward a few decades and you’d probably find corrosion at the end of some wires and new terminals being required – and that would be it. In comparison, Suzuki and Kawasaki were not so good, with Yamaha trailing in last.
So, was the move to 12V electrics a good move? Of course it was! And any Jap 6V or 12V system was streets ahead of anything that the British bikes carried…
