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Hey everyone!


Finally got my hands on the perfect scoot for my area.

It's a 78 P125X VNX. Kick start/battery.

After looking through a wiring diagram, I see some things appear wired together by a white wire:

Headlight (only comes on when the engine is running)
Horn (doesnt work)
Neutral Light (works)
Speedo light (works)
Front brake light switch (doesnt work)
Rear brake light switch (doesnt work)


Today I noticed that I cant get the brake light to come on(with engine off). I cleaned up both switches at the front brake lever, and foot brake. Still nothing.

What am I missing?
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The fact that the horn doesnt work would lead me to first check the battery voltage. 12v+ DC. If thats good, check if the fuse is blown. Check next to the battery for a white, barrel shaped fuse holder. Unscrew and theres 8a VW fuses in there.

If thats intact, I'd be curious to see if everything's connected correctly at the keyswitch.
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MJRally wrote:
The fact that the horn doesnt work would lead me to first check the battery voltage. 12v+ DC. If thats good, check if the fuse is blown. Check next to the battery for a white, barrel shaped fuse holder. Unscrew and theres 8a VW fuses in there.

If thats intact, I'd be curious to see if everything's connected correctly at the keyswitch.
So, i cant check the voltage until tomorrow, but the fuse is there and looks good. Here's a picture of the back of the ignition switch, and the diagram im using.[/img]
Forum member supplied image with no explanatory text
Forum member supplied image with no explanatory text
⚠️ Last edited by coastalviews on UTC; edited 1 time
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UPDATE: Found my multimeter. Getting 12v exactly at the battery terminals. Theres 2 white wires connected to 1 side of the brake switch, and 1 blue. Both are getting just over 11v to them. If i connect them, will that trigger the brake light?
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coastalviews wrote:
UPDATE: Found my multimeter. Getting 12v exactly at the battery terminals. Theres 2 white wires connected to 1 side of the brake switch, and 1 blue. Both are getting just over 11v to them. If i connect them, will that trigger the brake light?
So that will complete the light circuit. If that still doesn't turn on the light, your problem is either a cut wire, bad bulb holder or blown bulb.

Starting with the easy one, have you inspected the bulb to see if it's blown?
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MJRally wrote:
So that will complete the light circuit. If that still doesn't turn on the light, your problem is either a cut wire, bad bulb holder or blown bulb.

Starting with the easy one, have you inspected the bulb to see if it's blown?
The bulbs are brand new so its not that. I *think* maybe the switch is toast. I took it out and couldn't for the life of me figure out how it worked since neither side would move. After soaking it in wd40, then rubbing alcohol, and using an air compressor to blow it dry, it sorta moves a little when I really squeeze the brake lever. It doesn't instill confidence though.

After I gave up on the handlebar switch, i re-visited the foot brake. I was able to confirm that the wiring WILL trigger the brake light(without the switch), about 5 seconds before I accidentally grounded out the hot wire, and blew the fuse. So i'm done for the evening.

Thank you for the help so far.
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So your electrical theory is sound, just need to avoid shorting out the wires Razz emoticon

The front brake switch is unique as its cable tension driven. With a multimeter, connect each terminal end and look for continuity when you squeeze the lever WITH the brake cable tensioned!

The rear brake you can test the easy way, just with the terminals and one finger pushing the switch in and out.

It's rare that the switches fail. Usually it's the terminals or wiring which fails but, like anything, there is always a chance. Keep sleuthing and buy some more fuses!
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I've never been good with wiring. I just cant wrap my brain around it.

For instance: When testing the wires going to both terminals on the front switch, they both lit up the test light. How/why is that correct?

And when I was messing with the foot brake switch, the brake light lit up, but im not sure if the wires were touching eachother, or the frame.

What a mess. lol
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If the test light is lighting up on both legs without the switch being manipulated, you definitely have a problem there. It should be one hot wire (white) which then powers the blue when the lever is pulled. Then shuts power to blue when the switch is released. Easy on/off. If it's anything else, I'd look into your tester or ask someone to check your work.

Think of it like plumbing. Water comes in one way, through the switch, out this wire to this bulb and then to ground (down the drain). "Water" makes a circular path and shouldn't be going past certain points until you allow it (switches make contact.)
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Here's a few things to try.

Set your multi meter to continuity. This should give you a beep when you touch your two test leads together.

1. Disconnect your battery
2. Put one test lead to a good ground connection on the frame. Like center stand bolt etc.
3. Put the other test lead on the white wire terminal on the front brake switch. If you get a beep that's bad and means the white wire is grounding out somewhere.
4. Repeat step 3 but this time on blue wire terminal on front brake switch. Same thing, beep means the wire is grounding out somewhere.
5-6. Repeat 3-4 at the front brake switch wire terminals.

You don't want to hear beeps during these tests!

Check rear brake switch.
Unbolt the switch and inspect the rubber gasket underneath it. It may even be missing! If it's deteriorated it could allow the wire terminals to touch the rear brake assembly and short to ground there.

Good luck!

Hec
Check rubber gasket underneath brake switch.
Check rubber gasket underneath brake switch.
Underside of rear brake switch.  Remove bolt and spring to inspect brake switch rubber gasket.
Underside of rear brake switch. Remove bolt and spring to inspect brake switch rubber gasket.
The gasket under the rear brake switch creates clearance between the wire terminals and brake pedal housing.
The gasket under the rear brake switch creates clearance between the wire terminals and brake pedal housing.
⚠️ Last edited by Hec In Omaha on UTC; edited 1 time
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Hec In Omaha wrote:
Here's a few things to try.

Set your multi meter to continuity. This should give you a beep when you touch your two test leads together.

1. Disconnect your battery
2. Put one test lead to a good ground connection on the frame. Like center stand bolt etc.
3. Put the other test lead on the white wire terminal on the front brake switch. If you get a beep that's bad and means the white wire is grounding out somewhere.
4. Repeat step 3 but this time on blue wire terminal on front brake switch. Same thing, beep means the wire is grounding out somewhere.
5-6. Repeat 3-4 at the front brake switch wire terminals.

You don't want to hear beeps during these tests!

Check rear brake switch.
Unbolt the switch and inspect the rubber gasket underneath it. It may even be missing! If it's deteriorated it could allow the wire terminals to touch the rear brake assembly and short to ground there.

Good luck!

Hec
Ok!, good news and bad news. Just tested both switches, and dammit, they both work! The rear beeps when the brake pedal releases the plunger(as it should), and the front beeps when the lever is pulled in(as it should).

Im still waiting to see of the store is going to be open today, so I can buy some fuses.
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coastalviews wrote:
Ok!, good news and bad news. Just tested both switches, and dammit, they both work! The rear beeps when the brake pedal releases the plunger(as it should), and the front beeps when the lever is pulled in(as it should).

Im still waiting to see of the store is going to be open today, so I can buy some fuses.
That is good news! My money is on the white wire grounding out somewhere. According to your wiring diagram the white wire is common to your horn, and brake switches.
BTW you don't need a fuse to find a short to ground! Run the tests I posted above.

Hec
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Hec In Omaha wrote:
Here's a few things to try.

Set your multi meter to continuity. This should give you a beep when you touch your two test leads together.

1. Disconnect your battery
2. Put one test lead to a good ground connection on the frame. Like center stand bolt etc.
3. Put the other test lead on the white wire terminal on the front brake switch. If you get a beep that's bad and means the white wire is grounding out somewhere.
4. Repeat step 3 but this time on blue wire terminal on front brake switch. Same thing, beep means the wire is grounding out somewhere.
5-6. Repeat 3-4 at the front brake switch wire terminals.

With the battery disconnected, and wires removed from both brake switches, both white and blue wires are beeping during the continuity test. Ugh.
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coastalviews wrote:
With the battery disconnected, and wires removed from both brake switches, both white and blue wires are beeping during the continuity test. Ugh.
Now the hunt for the short to ground begins! Since you are getting continuity to ground on both the blue and white wires, I believe they got pinched together somewhere.
I suspect your problem lies near the brake pedal assembly. perhaps the rear brake cable was replaced at some point, and the wires got smashed between the brake pedal assembly and the frame when the brake pedal was reinstalled. Remove the brake pedal from the frame and reach in and pull out the blue and white wire out of the hole in the frame. You should be able to pull 8" of blue and white wires out the hole in the frame. They should be in a wire sheath together. Take a close look at the wires there. Also look at wires near the front brake switch as they run together there as well.

Good luck


Hec
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Hec In Omaha wrote:
Now the hunt for the short to ground begins! Since you are getting continuity to ground on both the blue and white wires, I believe they got pinched together somewhere.
I suspect your problem lies near the brake pedal assembly. perhaps the rear brake cable was replaced at some point, and the wires got smashed between the brake pedal assembly and the frame when the brake pedal was reinstalled. Remove the brake pedal from the frame and reach in and pull out the blue and white wire out of the hole in the frame. You should be able to pull 8" of blue and white wires out the hole in the frame. They should be in a wire sheath together. Take a close look at the wires there. Also look at wires near the front brake switch as they run together there as well.

Good luck
Hec
So I disconnecting the white, and blue wires anyplace theyre connected to something, plugged the multimeter to the foot brake red wire, and black to a bolt hole, and started plugging things in 1 at a time, until there was a beep.

Things like the front brake switch, indicator flasher, horn, didnt cause any beeps. But, things that have bulbs, like the speedo bulb/neutral light/taillight/ did beep, i assume because the bulb grounds the circuit.

How do I test those things for a short?
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coastalviews wrote:
So I disconnecting the white, and blue wires anyplace theyre connected to something, plugged the multimeter to the foot brake red wire, and black to a bolt hole, and started plugging things in 1 at a time, until there was a beep.

Things like the front brake switch, indicator flasher, horn, didnt cause any beeps. But, things that have bulbs, like the speedo bulb/neutral light/taillight/ did beep, i assume because the bulb grounds the circuit.

How do I test those things for a short?
Test for continuity to ground for the white wires, to the bulbs you mentioned, with bulbs removed from the sockets.

Also repeat tests while unplugging the white wire from the ignition switch.

Inspect blue and white wire insulation at rear brake light.

Hec
Check wires for broken insulation rubbing metal at the rear brake light where wires pass through light frame
Check wires for broken insulation rubbing metal at the rear brake light where wires pass through light frame
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Hec In Omaha wrote:
Test for continuity to ground for the white wires, to the bulbs you mentioned, with bulbs removed from the sockets.

Also repeat tests while unplugging the white wire from the ignition switch.

Inspect blue and white wire insulation at rear brake light.

Hec
Is that taillight wiring configuration the same throughout the years?? Mine isnt like that.
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coastalviews wrote:
Is that taillight wiring configuration the same throughout the years?? Mine isnt like that.
That's the taillight of my 1980 P125X US Spec.
Forum member supplied image with no explanatory text
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Hec In Omaha wrote:
Now the hunt for the short to ground begins! Since you are getting continuity to ground on both the blue and white wires, I believe they got pinched together somewhere.
I suspect your problem lies near the brake pedal assembly. perhaps the rear brake cable was replaced at some point, and the wires got smashed between the brake pedal assembly and the frame when the brake pedal was reinstalled. Remove the brake pedal from the frame and reach in and pull out the blue and white wire out of the hole in the frame. You should be able to pull 8" of blue and white wires out the hole in the frame. They should be in a wire sheath together. Take a close look at the wires there. Also look at wires near the front brake switch as they run together there as well.

Good luck


Hec
Im actually surprised at how good the wiring looks on this vespa. I don't know if it was ever replaced, or if it was just kept indoors. As i've been tracking down this grounding problem, i've been cleaning contacts, and hitting them with some dialectic grease, just in case.

Wiggling the wires on the back of the taillight housing(bulb inserted), led to intermittent beeping on the multimeter. I wondering if maybe the short is in there. Ill keep looking. Ive got a bunch of fuses on order. Hopefully I can plug things in one at a time, until the fuse pops.
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coastalviews wrote:
Im actually surprised at how good the wiring looks on this vespa. I don't know if it was ever replaced, or if it was just kept indoors. As i've been tracking down this grounding problem, i've been cleaning contacts, and hitting them with some dialectic grease, just in case.

Wiggling the wires on the back of the taillight housing(bulb inserted), led to intermittent beeping on the multimeter. I wondering if maybe the short is in there. Ill keep looking. Ive got a bunch of fuses on order. Hopefully I can plug things in one at a time, until the fuse pops.
While your inspecting wires, pay close attention to dreaded "Green Ignition Kill Wire". This wire can be found at the engine wire junction box, runs thru the frame tunnel to the ignition switch and handle bar kill switch. The green dye used eventually disintegrates the insulation leaving you with bare wire. If the exposed bare wire touches metal it will kill the engine or not allow it to start. My green wire looked great in some places and terrible in others. I ended up replacing the entire wire harness.

Hec
Green wire deteriorated insulation
Green wire deteriorated insulation
Kill switch
Kill switch
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coastalviews wrote:
As i've been tracking down this grounding problem, i've been cleaning contacts, and hitting them with some dialectic grease, just in case.
Where did you get the dialectic grease? That could come in handy when dealing with acquaintances who have political viewpoints opposed to my own.
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Finally got new fuses in today. I did notice that pulling the brake lever lights up the rear bulb just the slightest bit. Is it possible that the brake light is only supposed to work while the bike is running? Like the headlight?
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coastalviews wrote:
Finally got new fuses in today. I did notice that pulling the brake lever lights up the rear bulb just the slightest bit. Is it possible that the brake light is only supposed to work while the bike is running? Like the headlight?
If I'm reading your posted wiring diagram correctly, your brake light gets its power from the batt.Your headlight gets its power from the stator.
Make sure your battery is fully charged up and that the brake light bulb is good. Ensure that the bulb is inserted correctly into the socket. Check that all the brake light wire connections are good too. Can you read the voltage at the brake light socket when you hit the brakes? It should have the same voltage as the battery. If it reads lower then there is in issue with the wiring.

Hec
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Mystery solved. I'm an idiot. Facepalm emoticon

The PO had the stoplight/taillight wires backwards. I greased em up and put em back on the way they were, not seeing that they had the markings on the housing(which got covered by the grease).
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