Modern Vespa

Hey guys!

I've got a strange issue with the light switch, but maybe it's me, since it's my first small frame : When I'm on a specific setting on the two light switches, I'm unable to use the horn for some reason... Any clues for me?

I've attached pictures of my switch, light wiring and a photo of the wiring loom installation manual. If you see any issue with my wiring or if you have insights to fix this, let me know!

By the way, this small frame has been converted to SIP Vape sport.

Connections at the light seem fine; I'm guessing the issue is with the connections behind the switch.

Here's a picture of behind the switch. Let me know if you see anything suspect, I've followed SIP documentation, but maybe I missed something...

Yeah this ^

The horn is powered via the loom.
The switch grounds the horn circuit via headset ground.

I had to file off the new paint where the cover tabs land to get mine to work.

You mean that the switch is grounded through the actual switch cover!? This cover? How come it's not in the instruction… Sigh…! So I need to file off the paint arround the slots (see picture)? Thanks guys!

Check for continuity between the cover and ground.

edit: actually, if the kill button works it's grounded...

Very strange but kill switch it's not working 100% of the time... I've try removing painted arround the cover switch but doesn't seems to fixed the issue...

Do you have continuity between the cover and ground? This would affect the kill.
Do all the lights work?
Also, if I am not mistaken, on some of these small frames the horn grounds through the bulbs when they are on and to the black (grnd) when they are off. I had this all figured out years ago but I have lost my diagrams and Mr. Memory is well on his way out of the building.

Do you have ground from the harness connected to the plate that guides the cables?

Do you mean #10 on the SIP list he posted?

Quick update: I've continued my troubleshooting and confirmed continuity on the switch screw, the switch casing, and from the handlebar to the engine. So basically, everything looks good regarding grounds.

The tab that makes contact for the kill switch was slightly bent the wrong way, which was probably the cause of my kill switch issue.

Regarding the horn: all my lights are working properly, and all the light switches function correctly as well. The horn problem only happens when I have the most intense light setting on (rear, front, and high beam). In that case, the horn doesn't work for some reason.

Someone mentioned that my 12V horn might be drawing too much power when all the lights are on. What do you guys think? Should I switch back to a 6V horn?

Certainly worth a shot. I'm not sure if the SH diagram matches your system (it shows two greens at the switch and a red kill wire) but it shows the horn coming off its own coil so I don't see why the lights would affect it. Do the lights dim when the horn button is pressed?
Vespa electrics are weird.

Rear, front, and high beam? What do you mean by rear? Brake light, or regular rear light? High beam and front (you mean low?) are the same fed by 2 different wires, not 2 separate lights working at the same time. On a typical headlight bulb, high will either draw 5W more than low, or exactly the same (60/55, 45/40, 35/35, 25/25).

The brake light will draw 10W while the rear only 5W. So at most, if in high beam and braking, you'd be consuming 15W more than riding along in low beam; not likely enough to explain the horn not even emitting a peep, unless your stator is very weak. And even then, horn and lights would be competing for whatever juice there is, which would more likely result in a quack and weak lights than the horn being completely silent.

My guess is in a false ground or an incorrect connnection somewhere.


PS: is this still a 6V system? In that case, yes, a 12V horn is going to drain energy big time. No experience with those though...

#10 also connects to that bracket bolt, along with black from the harness that grounds the headset from the stator.

The headset will still beep to ground without that connection, but beep-ground through greased bearings is not the same.

That Vape should totally handle all the electricals, including a 12v horn.

Just to add more information on my setup :

-SIP Vape Sport 12v AC
-SIP Speedometer/Rev Counter 2.0 (Analog + Digital)
-SIP/Koso temp sensor
-SIP Speed Sensor (Electronic speed sensor)
-SIP Fast Flow 2.0 with electronic power reserve gauge

I don't think these accessories consume a lot of power, but just in case.

"By the way, this small frame has been converted to SIP Vape sport. "

I apologize, I somehow totally missed this line.

I did a voltage test, my horn typically receive 12 to 13 volts depending of the RPM of the engine (I'm on AC). But when the headlight is « on » the voltage drop between 9 and 10v. So when I say « the horn is not working » it's probably more accurate to say that the horn is not receiving enough juice…

I'm using SIP wirring loom, the horn is wired in parralel, so I dont think it's an issue with wires or grounds. On an AC 12v conversion Vespa, is it something that you saw previously?

By the way, i'm running a 45w bulb on the headlight…

I've converted both my bikes to 12v electronic and both still have the 6v horn which works. No horn issues. Have you tried swapping the poles the horn wires attach to at the horn?

Thanks for the reply! Is there really a "right way" to plug the horn? I did not think about that... I've bought new LED bulbs that consume less juice. I'll try this during the weekend

No clue just spit balling!

Doesn't matter.

Guys, I've found my issue… Headlight bulb was pulling too much juice from the system… (It was a 45w bulb) I've switch every bulbs to LED and the horn is working fine regardless of the light switch setting.