I am recommissioning an old CT90 k1, sold in the USA in 1969. I've colourised the wiring diagram to make it easier to read, and you can get a copy below.
When the CT90 k1 was released in the US, Honda fitted it with the wiring for turn signals - presumably in anticipation of their usage becoming a requirement in the US (which they did in the 1970s) - however, the lamps and relay were not included. The diagram is on the left shows the wiring as fitted to the standard bike, and the right includes the turn signal equipment added.
(left) without turn signals / (right) with turn signals
I'll be retro fitting the winkers, which as you can see is a straightforward job since the bike came with (redundant) L/R switchgear, all the necessary wiring and even a turn-signal indicator light in the speedo.
The CT90 K1, which succeeded the K0 model, came with several design improvements, and to mark the new design Honda restarted the serial numbers stamped on the engine and frame at zero, hence the references to Frame No. 000001A on the parts and wiring diagrams for the K1 models. In practice, from this point forwards, Honda prefixed the serial number with a single digit number indicating the year of manufacture and resetting the numbering for each annual revision to the range, starting with the 200000 range for the K1, 300000 for K2 and so on (after a few years they gave up on this idea and went back to a standard sequential serial number).
The K0 and K1 models used a very similar wiring arrangement, the main difference being the K1 included a switch to activate the rear stop light when the front brake is used. There were other modifications made to later models, including the addition of a kill switch and a change to 'always on' lights, but much of the K1 wiring will be familiar on later bikes.
It is easier to follow the wiring diagram when each of the subsystems are drawn in insolation. See below for the separate diagrams for the charging, ignition and lighting system:
ct90 charging, ignition and lighting systems
There are lots of similarities between this bike and the C90 I've already written about, but I'll include some information on the special features added to the CTs and details of the repairs I do. One of the early jobs is to make a replacement wiring harness, of which more later