What the hell is this?

[rd400canuck]

As I was looking at wires trying to sort my signal light issue I noticed a connect tuck up under the frame that was loose. I see where it came from and pull the module out. I cant find anything like it in the wring schematics I see online. Anyone know what this?

[SoCal250]

I believe that is the headlight relay. (Canada only, not US models)

EDIT:
Make sure you're using the Canada model wiring diagram. The CAN and US models have different wire harnesses. The wiring diagram can be found here: THE TECH LIBRARY »Yamaha Factory Specs and Info »Yamaha Wiring Diagrams

The Yamaha part # for the relay is 360-81590-10-00

[rd400canuck]

That's weird.... wouldnt the lights not work if it was completely disconnected?

[Greaser Greg]

May be an automotive turn signal relay.

[rd400canuck]

well going by the CDN wiring diagram (thanks socal) it appears to be a relay to turn the head lights on and off. There is actually a switch on the right handlebar that does this and it works, too.

Beats me... everything works as it should so I dont get it.

[Striker1423]

I do believe some of the Canadian and British bikes (RD350's had it if I recall reading this a while back) had a secondary running light built into the headlamp dome near the bottom? It was just a small bulb in its own socket. That way with the switch off you still had a daytime running lamp on at all times due to European and Canadian regulation at the time. Just spit-balling here, but perhaps this is what the relay was meant to do? If not, I guess I wouldn't worry about it too much.

EDIT: It was bugging me so I asked on the acRD forum where they deal with a lot more EU spec bikes lol. I'll see what they say.

EDIT2:
So the bulb I was thinking of was a parking lamp for some UL and EU bikes. Was not a running light. Well I tried haha. My guess is Yamaha added it for some reason. What it is... I dont know.

[Clem]

Looks like the head lamp relay on my Daytona. On the US Daytona it keeps the headlight off until the engine starts up.

[Alain2]

Signal cancel unit?

[rd400canuck]

There is another module that is stuffed up in the neck of the frame just above it that I think is the cancel unit. I'm beginning to wonder if the bike was wired not to use it by someone in the past. When I changed the light bucket I had to under all the connectors in it then redo them. I just went by color of wires and looked at a wiring diagram but not of a canadian RD... it was a US color schematic. I didnt notice or see any wires in there that had been altered in any way... they all looked stock and untouched. I wonder if it's possible to connect the wires in a way that negates the existence of that relay.

I found that on/off switch for the lights odd.... I wonder if its purpose is to turn the headlight in when the engine is not running and when running, the light is turned on regardless of the switch position by this relay.

[SoCal250]

As I said above it's the headlight relay. As Clem correctly pointed out, it prevents the headlight from getting power until the engine is kicked over.
The light switch on the handlebar overrides the relay and acts as a master power switch. Refer to the wiring diagram.

I would guess that if your bike is not functioning like this then it probably has been altered by someone in the past to bypass the relay. If everything else is working OK and you ON-OFF handlebar switch works then I wouldn't worry about it too much. Just leave the relay out of the system.

[SUPERTUNE]

Our U.S. made '79 Daytona RD400's have no headlight switch and have a relay to turn on the headlight once you kick start it and see's voltage from the stator to trip the relay and turn on the headlight.
Chuck

[rd400canuck]

ok... you guys were right. It's a relay that turns the headlights on when the engine starts. I traced the yellow wire directly to the engine. I unplugged it and sent 12v to it and it flickered and made a noise. I cleaned the leads and connector to the module and tried again and  bam...  the lights turned on.

After seeing the canadian schematics it seems so obvious now. Weird set up though for a jap motorcycle... that Ive seen anyways. I'm used to headlights turning on with the ignition switch and not having an option to turn them on and off when the engine isnt running.

Thanks again guys... the bike is slowly getting sorted and put back to proper stock working condition :)

[SoCal250]

Glad you got it sorted out

[EE]

Because a dead battery leaves you stranded on US 400's because of the battery energized charging system they use.. on my old Daytona and at least one other Daytona i put an earlier 400 handlebar switch on instead of the non headlamp switch Daytona piece and bypassed the relay because if you got a good kick in the headlamp would come on and start draining the battery while your trying to start it.. no relay= no extra current draw while trying to get it started.

[SoCal250]

Because a dead battery leaves you stranded on US 400's because of the battery energized charging system they use.. on my old Daytona and at least one other Daytona i put an earlier 400 handlebar switch on instead of the non headlamp switch Daytona piece and bypassed the relay because if you got a good kick in the headlamp would come on and start draining the battery while your trying to start it.. no relay= no extra current draw while trying to get it started.

Same here. 1A1 handlebar switch on my 2V0 and no relay  ;)