Vespa 50s / 100 engine. Rear light and running problem.

[h11poc]

Hi all. I finally started my vespa project this weekend and have a couple of issues. The first is the brake light and rear light are constantly on. Pressing the brake pedal makes no difference at all. If I remove the earth wire from the brake light both lights still remain on. I removed both wires from the brake pedal switch and still they remain on. I have the yellow wire to the bottom bulb and the blue to the top bulb when looking at the rear light. I used a new 50s wiring loom and added the brake pedal loom section from the old loom.   All the lights work normally on the headset switches, horn works, high/low beam/ pilot light and kill switch. The wires are attached at the junction box to match the colours.  I am not sure whether the brake pedal switch could be at fault ? Either way both rear lights are permanently on. 
The second issue is the scooter starts first time with the choke out but dies when you apply throttle. It will tick over with the choke off after a couple of minutes but again dies when the throttle is pulled back unless you do it VERY slowly and it will rev slowly.  The carb has been rebuilt , the jets are fine and the stator plate looks new and shiny coils. There is fresh fuel in there too. The air/fuel mixture adjusted correctly and slight adjustments to that make no difference.  There is very good spark from the plug so I am stuck as to where the issue lies. Could it be Earth issue too??? or is that done with the coil attached to the frame?

Any advice on either issue would be most welcome .

Paul

[jbcollier]

First, get yourself a simple 12v test light. Not the ones with an LED, get one with a bulb. Next remove both power wires from the tail light. Test both for power. It can be normal to have power to the tail light all the time depending on the harness. If you have power at the brake light wire, trace it back to find out where it is coming from.

It may also be a ground issue. Attach the test light lead to the engine case and touch tail light ground with the probe. Lights up? The tail light is not grounded. Run a ground wire from the engine cases to the body. Scrape the paint from the around one tail light mounting nut and use a serrated locl washer to get a good connection. Apply vasoline after to protect from corrosion. Test again.

[h11poc]

Appreciate the help and thank you. Just one thing i cant work out. The brake pedal switch !! That blue wire is providing live to the bulb which I can see. Howeveer the blue from the brake light goes to the junction box to meet the blue from the stator and from there another blue wire goes to the bulb. Surely the switch is not relevant as the blue wire to the bulb is ALWAYS live and no matter what switch is attached will not change that... Unless TESLA worked for Vespa then someone explain how a brake light switch in the pedal can alter the voltage going to the brake light bulb when effectively it is straight from the blue coming from the stator .  Would it not have been better to have a blue from the stator running directly to the brake light switch and then on the other terminal on the switch another blue to the brake light. Then when the pedal is pressed and connection is made the bulb lights up. Surely this is way more logical and simpler than the current system?? Unless of course someone tells me the blue from the stator plate is not live...

[jbcollier]

On low-output, four coil stators, often the brake light circuit was shorted to ground to turn off. On six-coil stators, the power would go to the switch then on to the bulb. If your switch is "off" when the pedal is released, and "on" when the pedal is depressed, then blue from stator to brake light switch and a separate wire back to the bulb.

[h11poc]

I must be four coil stator ?? Its a vespa 100 engine.. Saying that , how would I even tell?? But I agree running a blue wire to the switch and then back to the bulb and simply joining the circuit when pressing the brake pedal seems the way to go.

[h11poc]

Ah - also both bulbs are earthed naturally from the bulb holder.. I can see that clearly... What is actually up with rear light vespa wiring?? None of it makes sense to me at all...
Surely to god others out there have been stumped by this enigma?

[jbcollier]

On a four coil system, the bulb holders are still earthed.

How many, and what colour are the wires out of your stator?

Is there a regulator in the system?

[h11poc]

From my stator I have Blue, Yellow, Green , Red and Black. I am not sure if I have a regulator. It in theory should be the standard vespa 100 stator and wiring which I believe is the same as the Vespa 90. The frame is actually a 1967 50 Special but this should not make a difference to the wiring as the headset is three speed 105mm headlight which makes me think its also from a vespa 90
To be honest I cant work out this earth system as it appears it is only earthed at the headlight switch, the headlight bulb holder, the junction box and then again at the rear light bulb holder next to the rear light bulb.

[jbcollier]

Here you go:

www.scooterhelp.com/electrics/wiring/V9A1.pdf

The blue circuit is shorted to ground when the pedal is up. You need a normally open brake light switch (contacts closed when pedal is up).

[h11poc]

Ah thats the wiring I copied to create the loom in the first place. have it exactly wired like that. But then my switch is probably the wrong one !! I shall also take your advice in making a better earth connection from Engine casing to frame and then again from frame to rear light Earth .

As for the poor running and dying when throttle??? maybe fuel tap ?

[h11poc]

Just checked and have the correct switch - can see the contact is open when pedal pressed and closed when up - Has to be this earth then

[h11poc]

Totally lost guys - really need help. Just so gutted after so much work it just isnt right. This damn brake light. I have the right switch but the earth and blue are always connected regardless of the switch position because the earth from the brake light is linked with the earth to the junction which means its always earthed regardless? Should the earth from the brake light switch go directly to the rear light and not join the other earth wire for the main lights etc. If so then how is the tail lamp earthed??? is this through the earth at the junction box and then the headlight switch. The wiring diagram shows all the earths connected together which would mean it is impossible to break the circuit frm the brake like switch . i am tearing my hair out here trying to work out just what the hell is supposed to be wired where.
To cap it all , when the scooter starts which is first time the slightest throttle kills it. I have seen fuel from the tap when it is disconnected from the fuel hose but I dont see much fuel going down the hose when connected. Its a clear host and I would have thought it would be fast....
before i lose the plot and kill a 1967 50 special with a 100 engine fitted I plead for some help and advice.

[jbcollier]

Here are the two possible wring layouts for your scoot:

1. stator power -------- brake light switch ------- brake light bulb -------- chassis ground (brake light switch is "on" when pedal is depressed)

2. chassis ground -------- brake light bulb -------- stator power -------- brake light switch -------- chassis ground (brake light switch is "on" when pedal is released)

Which do layout you have? is the brake light switch the correct one for your layout?

[h11poc]

Thanks jb. My connecti9n is broken when the pedal is pressed. I actually pulled out the loom and ordered another one for a Vespa 90 as that is effectively wha my scooter is. I also ordered more bulbs as the two rears are 6v 18w and that’s way too much. I bought a flywheel puller and will check the stator plate too as that’s possible causing the running issue with timing way off. I think after fitting the correct loom, correct bulbs and making sure all the grounds are good i will come back and let you know what the issues are...

[h11poc]

new loom fitted and new bulbs to correct wattage. New switch Italian made one also fitted. All wired up and the same issue. So I now think it may be the stator plate? Maybe the earth in there messed up or a coil has failed? That would also explain the issue with the inability to rev and cutting out.
Does anyone have a v100 (v90) stator plate??

[exmayor]

Had the same issue with my ‘64 V90. Found stop on pedal was broken. Couldn’t find any reason for it. Found a replacement pedal.

[jbcollier]

You need to test the circuits and find what is wrong. Use a simple test light and check out the circuit.

[h11poc]

Thanks JB - When the flywheel puller arrives I can do that - i think you put a guide up on another thread so I'll find that .
In the meantime if I need a stator where can i get one? Ive looked and am unable to locate one.
Can I remain at six volts and go to electronic ignition?? or will that involve changing more than the stator?

[jbcollier]

Here is my understanding of the situation:

- you have two problems: brake light on all the time, and it dies if you give it throttle.

The problems may, or may not, be linked but it is best to approach them individually. I would suggest starting with the brake light as it is a straight forward diagnosis.

So to start, the light is on. Therefore the stator may be working just fine as you have power. The problem is that the power is not being properly controlled.

The first thing to do is go to the tail light and pull off the wire for the brake light. Now test for power from the wire and the wire terminal. Which has power?

[h11poc]

Yes, the scooter dies when I rev. The brake light gets brighter... I took the stator plate out and to be honest it all looks ok. I will replace the wires if need be .
After I put it back on i shall carry out the test you mentioned above.