Turn signals - or 'winkers' as Honda refer to them - became a standard fixture with the 1973 CT90 K4 model. This followed the introduction of federal legislation in the USA that made turn signals mandatory on all cars and motorcycles.

Retrofitting

Retrofitting turn-signals on the older models is not difficult since - prior to 1973 - Honda had supplied them as an optional extra and consequently there are harness connections for the relay and lights and the switchgear includes a L/R indicator lever as standard.

The main additional parts you need are shown on the left below:

winker assembly replacements

Lots of Honda bikes from this era used the type of winker assembly fitted to the CT90s (see above), so hopefully you will not have trouble finding some decent secondhand versions.

The standard CT90 winkers have a single power supply wire and the earth (ground) connection is made through the metal bulb's base connection to the handlebars (the earth connection to the battery is actually via the headlight's green wire harness connection). Some of the light assemblies come with two wires and will need modifications if you are going to use them:

Note that if the lights were were designed to work with the dual filament bulbs used on bikes where the indicators double up as running lights, the bulb holder does not fit a standard bulb. If you want to stick with standard bulbs, you can swap over the bulb holder from another light to get them to work. You'll need to keep an eye out for spare single-wire assemblies to use for parts (luckily badly corroded, damaged or incomplete lights often sell for pennies).

I managed to cobble together four good winker assemblies from three cheap pairs of lights purchased on ebay (the listings didn't mention which model the winkers were from, which is probably why they were so cheap). One set came attached to the correct stand-offs to fit onto the top yoke, which was a stroke of luck.

rear winker stay

A bracket is needed fit the rear indicators onto the rear mudguard. The correct part is 33602-053-650, but it is no longer available. A similar bracket was fitted to the C70 (33601-087-650) and - at the time I did mine - was still available from David Silvers. This part can be made to work, but you have to drill additional holes to fit it.

If you can't fit the rear lights this way you might be able to get hold of the rear tail-light bracket used on later bikes which has built in stand-offs for the rear winkers.

Winker relay

The last job is to fit a winker relay.

This is the device that causes the turn signal lights to flash on and off. The contemporary part has 3 terminals: the red (live) wire connects to the B/Battery terminal , the grey wire from the indicator switch goes to L/Load and the E/earth terminal is earthed to the frame.

Some small Hondas of this era used a two pin relay and these work using a bimetallic strip, but the the three-pin relay shown above uses an electromagnetic switch. They are not easy to find any more but, if you do get hold of one, note that they are designed to work with 2x 18 watt bulbs, as noted in the rating information printed on top of the relay case. If you don't fit the correct wattage indicator bulbs the flasher will not work correctly.

Luckily cheap electric flasher relays are readily available and are not fussy about what wattage bulbs are used. The version I acquired was exactly the right size to fit in the case of an old (broken) OEM flasher case I had, so I removed the internals of the old one and inserted the new flasher unit: this keeps the original look and I can reuse the bracket to fit it next to the battery.

The "X" terminal on the new flasher unit connects to the red (live) wire in the harness and (L)oad terminal goes to the grey wire that connects to the turn signal switch. I put a bit of shrink-wrap on the "P" connection as this is not needed (it is there to power a "pilot" light to signal the winkers are operating, but the CT already has wiring in place for this).

That's it - job done!