Modern Vespa

Hi all -

I've taken my Vespa apart for painting...again. In putting it back together, everything seemed to work fine, except the headlight (main bulb). I tried replacing with a new one and still no luck. The little marker bulb in the headlight works OK.

Then, today, as I was changing doing a coolant flush, I ran the engine for about 15 minutes, then turned off the bike so it could cool down.

In the meantime, I took out the battery, added leads for a battery tender and also unclipped and rerouted the cable for the immobilizer under the coolant tank.

Then....WTF!

I turn the key to on, dash lights up but I get no lights in front or back. Turn signals work but headlight and taillight don't. When I pull the brake levers, the brake lamp doesn't light. I cannot start the scooter.

I checked every single fuse. All are fine.

Can someone with some understanding of Vespa electricals help me here? I'm up against the ropes

A little video of when things were going well...https://www.dropbox.com/scl/fo/7zluuqq81oov1p0y705kr/h?rlkey=19efai9d184yzccif75kxl1oa&dl=0

Have you checked the fuses visually or measured for continuity with a multimeter or test lamp?

Visually

GermanGTSDriver's point is that visually is not an adequate check.

Re-look at this area and check around your work, have you nipped a wire, if it was running before I would start here and as GermanGTSDriver really need to check fuses with a meter even if they visually look okay😉👍

Please put the model year of your GTS300 in your profile, as the circuits vary.

Thank you guys! Will check fuses with a meter and look around my work. Quite sure I didn't damage any wires. Maybe the positive lead of the battery tender is touching the frame, creating a short to ground? I'll have a see…

Added my model year to my profile as suggested

The circuit diagram you want is here: https://manuals.wotmeworry.org.uk/Vespa/GTS300%20Super/

I appreciate the diagram. I think it is also depicted in the GTS Shop Manual, which I have. Unfortunately, I'm not electrically-minded and have no idea how to read it

That's pretty much my main reason for asking for your guys' help.

Start with the simplest first: Have you measured the fuses in the meantime?
If you want us to help you, we can only do this step-by-step and if you give us feedback on the steps we recommend.

Thank you for staying with me friends...

Good news to report! The Vespa runs!!

It turns out that yesterday, when checking fuses, I must have made a poor connection when reinstalling fuse 9, which gives power to the tail light and also apparently the little bulb in the headlight (correct me if I'm wrong).

Hence, the lights didn't work, and without a working brake light - impossible to start.

Because the scooter is up in years, the contacts seem to be oxidized. Today when following your advice and testing the fuses with the multimeter, I wiggled them around and everything started to work....

EXCEPT THE HEADLIGHT

This was my initial problem, which led me to checking fuses in the first place.

So far, I tested the following:

1) New bulb with leads directly to battery - lights up good
2) All fuses checked with multimeter - all good
3) Checked high/low beam switch with Ohm setting - working properly
4) Tested the plug and wires that go to the headlight bulbs socket. No power there. I have brown, black, and purple wires on the plug as in the photo attached.

I'm guessing the next thing to check would be the relays in the front above the horn? If so, can I bypass the relay somehow, by bridging with a wire?

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Remember - on the 300 the headlight only comes on if the motor is running and 'happy'.

Today, I was at it again:

1) Checked both relays above the horn, according to the shop manual. Even though they look corroded as all hell, they work fine.

There was no continuity between the pair of terminals. Then, when I applied current to the other pair of terminals, there was a click and there was continuity.

The manual didn't mention the orientation of the positive and negative leads so I put them any which way on 85 and 86 of the relay.

I switched the position of the relays left-to-right, just in case.

2) At the headlight plug, I thought maybe corrosion was a factor, so I cut off the plug and tested voltage directly at the wires. There was nothing - well a tiny current on the purple wire (pictures).

Where do I go from here?

P.S. Today it seems I made negative progress - this may be unrelated but now my cooling fan doesn't turn on.

I've been doing a coolant system flush to get rid of rust and degraded hose bits, from the scooter sitting in storage for 3 years. The last time I was running the system (2 days ago, the fan kicked in just fine).

Today it wouldn't turn on, even when the temperature got super hot.

I know coolant is circulating because I bleed the system at the thermostat screw and it also gets hot in the reservoir.

I know the fan works, because I jumped it to the battery and it spun up just fine.

I also worked fine the other day, but not today.


PLEASE, PLEASE, PLEASE HELP!!!!

You said you tested for voltage but according to the picture your DVM is set on the current scale not voltage scale

Looks like it's set to 20V scale to me

Your right. My eyes were tired

What do I check next friends? Could the relays be problematic even though they passed my initial test? It was only after I took out the relay for testing that the fan stopped working.

Any idea which relay is responsible for fan? Headlight? Horn? The service manual doesn't make that clear, only says that these 2 are responsible for them.

My horn works.

Try this: With the meter on the brown wire as in the second picture, and with the scooter running so that the headlights should be on -- switch the high beam switch on and off a few times and see if 1) the meter changes, and 2) the headlights (either high or low) work at all.

The "0.52" volts reading puzzles me. Is there corrosion somewhere?

The 0.52V on the purple wire is bleed from the circuitry inside the headset for the blue hi-beam tally lamp.

The headlight will NOT come on without the engine running.

Open ground wire? With the scooter key OFF, measure the resistance from the black wire in the pictures, to the negative terminal of the battery.

Ok. Thank you JKJ.
What are the different possible scenarios? And what would I do in each case?

Are you still testing for the headlight with the engine OFF or the engine ON and running?

I'm just trying to get a better picture of what's going on. It would be a lot easier if the scooter were in front of me! As for the purple and brown wires, I'm trying to see if either the high beam or low beam is working at all. If one works, the problem may be a broken wire or the Hi/Low switch. I know you tested the switch with a meter, but the contact could be intermittent with a faulty switch. Exercising it on & off may either fix it (temporarily) or completely break it, in which case it's a likely culprit and should be replaced.

A broken ground connection could be the cause, too. The headlight assembly doesn't appear to be grounded through its shell, like some are. Instead, the grounding has to come through the black wire. Resistance greater than about 1 ohm between the end of the wire and the battery indicates a bad connection or broken wire somewhere.

I'm testing with the scooter running. I'll test again tomorrow around this time (maybe an hour later) and can give feedback in real-time, in the event one of you is available and can stand by to guide me. I could either post here or send by WhatsApp, if you want to give me a number. But no pressure. I'm not trying to make my problem a problem for everyone 😉

When you're taking resistance (ohms) measurements the scooter should not be running. It's best if you also disconnect the battery. (Don't measure resistance on a live circuit.)

You need to post here so everyone can see and follow the problem and maybe help solve it

Tests at the headlight relay:

With ignition off:
Grey wire should have permanent +12V on it.

With the ignition switched on, but the engine not running:
Yellow/Red should now have +12V on it. So should Blue/Black.

With engine running, Blue/Black should be at 0V (the relay coil is grounded by the ECU when the engine is running), and the Grey/Red should now be at +12V and the headlight should be on.

If all above is OK except the headlight is still of, then the switch needs replacing, or perhaps just the connector at the back of it re-seating.

Refer to the circuit diagram to see why the above should all hold true.

Thank you so much for that! I will run the tests and report back.

Which of the 2 relays is the one responsible for the headlight, right or left ?

And which one is responsible for the fan?

An aside I'm mentioning because of your comment about oxidation: I've had great experience using contact cleaners. Maxima makes a readily available product that can work wonders. The best I've found is Deoxit but it's harder to find. Using Maxima contact cleaner on old switches and electrical connections has really helped me out.

It varies 50-50 from the factory - it's the one with the wire colours mentioned above.

Fantastic. Thank you.

And thank you for the advice about contact cleaner - I was managing to clean the pins on relays/fuses but was having a hard time with the seats in the fuse holders. I'll pick up some contact cleaner and head over to work on the Vespa in an hour or so...

Will report.

Hello friends --

Good news...the light works!!

I swapped out the front relays for 2 new ones, and just like that - got power to the headlight wires. Then connected to the headlight lamp - and all good

I'm not sure what was wrong with the old relays - I tested them according to the Shop Manual: (1) made sure there was no continuity without power applied (2) then applied 12V and heard click and got continuity. Who knows what that was all about.

I haven't checked if the fan works yet, but I suspect that it does.

After I got the headlight to work, the small marker light in the head lamp and the rear lamp stopped working again. This was after I removed the fuses and sprayed everything down with contact cleaner.

I removed the fuses again and saw there was dry corrosion/buildup on them. So I scraped it off with a sharp knife and everything started working beautifully.

I used CRC electrical cleaner, as it was the only one I could get my hands on quickly. I'll order the Maxima one, for future use.

For the sake of completeness, I carried out the recommended checks and would like to report my finding below:

1. Open ground wire? With the scooter key OFF, measure the resistance from the black wire in the pictures, to the negative terminal of the battery.
The resistance I got was 00.6

2. With ignition off:Grey wire should have permanent +12V on it.
It sure did, actually around 13.5V in my case

3. With the ignition switched on, but the engine not running:
Yellow/Red should now have +12V on it. So should Blue/Black.
Yellow/Red had 12V, as for Blue/Black I do not have such a wire (see photos)

4. With engine running, Blue/Black should be at 0V (the relay coil is grounded by the ECU when the engine is running), and the Grey/Red should now be at +12V and the headlight should be on.
Again, could not located Blue/Black wire. The Grey/Red wire read 0

Thanks for all the help guys. If you want to explore further why my wires differ from those that jimc mentioned, I'll be happy to take some more readings.

Peace.

White/Black in your case, not Blue/Black. Perhaps the circuit diagram has a misprint of Bl (Blu/Blue) instead of Bi (Bianco/White). Or they just used a different colour 'because'.