Modern Vespa

Looks like the end is near!

I tried the cosa gauge first, and the needle bounced around with the revs like before.

Then I tried the original gauge fitted with the diode, and the needle went to full! (This is the one that had become unresponsive). The needle moves slower than the other (as if with more inertia), but it still moves to the left when twisting the throttle. In the vid below, the needle moves with my pushing the buoy with a screedriver.

I noticed while driving that there's still a nudge to the left when accelerating hard or dropping a gear, but at stable speeds or at idle, the needle seems to stabilize at the right position on the gauge scale.

I call this a win, because it seems to provide a correct reading whenever at idle at a red light or at a stable speed, which is most of the time I check it anyway.

I wonder if, in order to make the needle not react at all to variations in the rev range, a different module could be added to the circuit that would suppress any current value above what idle provides (since the gauge seems to be calibrated for such a value), but without the constant resistance of a resistor. Like a tiny regulator....

Still trying to figure out why variations in revs affect the gauge readings. I checked the regulator in case it was out of whack, but apparently not. Around 9.5 to 10.5V at idle, and up to 12.9 in the high rev range. So seems fine.

Now looking into a way of shaving off the voltage above 10V arriving at the gauge, since that's the range that seems to pull the needle to the left.

I finally managed to get the oil reserve sender to work; details here:

Since I've been asked politely to look at this, I now have a question. Apologies for resurrecting the thread. 😇

To state the obvious Frank N. Stein, your multimeter needs a battery change. That may rule out potential inconsistent readings.

Secondly, I need to you to put your meter into Vac range, lowest you have will suffice, and measure the positive and negative rails at the fuel gauge, after the diode. Not elsewhere, cause that's where we're hunting the ripple at. And of course, report back with a photo if possible. Do the measurements at idle and at open throttle.

Thanks for having a look.

1. Yes, the old multimeter was traded in for a new one that beeps. More more satisfying when checking continuity

2. Regarding testing in the V AC range, you do mean touching the multimeter contacts to the 12v in and ground points, and checking the reading at idle and wot, right? To check the range in current regardless of the fuel level.
I think I answered my own question.

I'll try to check it out tomorrow evening if I can, and circle back.

I'm gonna illustrate on this photo, although I understand it's not the cluster you're having difficulties with. But it's the same principle, nevertheless.

Just had a thought, measure the DC behind the diode as well please.

Ok, so I finally managed to get the tests done, and film them all, but now vimeo demands biometric age verification to upload videos, so they can eff themselves with a wire brush and I'll post pics instead

Here's the setup:

Underside of speedo (not quite as neat as the Piaggio version ):



Hot wire (red) to 12V feed and black wire to ground:



Same wires connected to the 12V and ground connections under the gauge:





Test bench:



AC Readings at idle:







DC Readings at idle:







AC Readings at WOT:







DC Readings at WOT:

Who else sees blue boxes instead of pictures?

Before I get a full understanding of the instrument connection (would have been much easier if I was there 😂), I can see that needle moves further to empty when the engine is running Vs when it's not. Polarity mismatch is my initial thought, but let me digest the images first.

Maybe you can upload the videos to google drive?

Works fine for me. Maybe clear the browser cache for last 24hrs?

In the box it says 'content not viewable in your region'.

Was just wondering which regions are blocked.

I always disliked the UK providers content filtering, while I was sailing around it. Perhaps your provider is not loading these particular photos, depending where they are hosted.

For an example, MV could be paying for hosting provided by GoDaddy (just an example). GoDaddy has servers at different geographical regions, and can dynamically assign any of these for storage. Your provider may not like a certain regions, so blocks access to servers located there. Result, the content perfectly benign, gets filtered.

You can test fix this by proxying your traffic via a public proxy in another country (not on UK's the blacklist), or VPN-ing.

Looks like it's US only

That's strange... And if it IS the provider it's pretty scary. . I uploaded the pics to imgur so I could reorder them in between blocks of text. Nothing offensive in there; no mean tweets to get anyone in trouble with British authorities for wrongspeak

You could evade geographical restrictions using a vpn as mentioned or the tor browser. Never mind, I'll post the pics separately uploading them directly to MV.

The setup: to gain access to the gauge's windings and still power it through the stator, I opened the speedo and "bridged" the 12v and ground prongs in the connector with the screws connecting these circuits to the windings. Red wire carries the 12V AC; black wire is the ground.

Here we go,

At IDLE, AC readings:

At IDLE, DC readings:

At WOT, AC readings:

And finally,

At WOT, DC readings:
(does "WOT" remind anyone else of Captain Sensible? Say captain, say wot? )

Can you confirm that this is how your gauge is wired "internally"?
Also, looking at this orientation, which contacts are +,GND and Float respectively?

That's not off the table. The speedo wiring was not mated to its original loom; it was wired by trial and error to function with the Piaggio sender via a homemade loom. This is the only setup that actually gave me a progressive movement of the gauge needle in accordance with the fuel tank float. Only issue is that the needle positions itself correctly at idle (with regards to the gas level), but dips as soon as I rev. Yikes, I avoid google products like STDs.

Hope this works for everyone:

https://streamable.com/71xyii

https://streamable.com/w97qrc



Yes, this is correct ^^^^

If of any use, I can take pics of the windings without the metal base. Basically, the thin winding wires end up on each stalk, and connect to the loom via the screws. I'll post pics of the internals later today.

Ok, we're on to something now.
Just confirm exact Float location please, before doing any mods.

This is what I'm struggling the most with, trying to wrap my mind around the situation.

If I understood correctly, in one of the previous posts you've mentioned a few things:

- Resistor is ~5.1R (Ohm), which matches it's markings, but you mentioned that is off-spec. What spec was this based on? Maybe I just misunderstood.
- Resistor changes value of the readings when wired in. This is correct, but how it is wired in, affects how the readings change. If wired in series, total resistance will be the coil resistance + resistor resistance. If wired in parallel, then the total resistance will be the result of the this equation: R=Rx*Ry/(Rx+Ry). Usually this equation results in value lower than the lowest of the two.

Your gauge should electrically look something like this, but not exclusively:

Sorry, by saying "correct" I meant that "Float" was closest to the correct screw.

Sorry, that post dealt with 2 separate gauges: the old one (which is currently in use), and a cosa unit, which had a 178 Ω resistor installed to replace the original 180 Ω, and gave inconsistent readings.

Regarding the current gauge, this part still applies: The diode was added in series later, and made the difference in that the gauge started "working".

Hope this helps.

I'll post pics of the internals and check the resistance of that particular resistor as soon as I get to the garage.

Ok. You can safely remove the diode.

Where does the resistor go? Needs to go back to it's original place.

The diode was added in series between the resistor and its previous position on the post. The connections vis a vis the windings haven't changed; the diode has just been wedged in.

Hope the pics to come will tell a clearer story.

If there's no insulated copper wire coming from yellow post, indicated here: Fuel gauge issue on an exotic P200 (Post 2763068) then I need you to:
- measure the X and Y resistances (resistor and diode should not make a difference), 200ohm range on your device will suffice,
- measuring between X & Y (outside posts a.k.a. excluding the shared post) will result in total resistance of X+Y previously measured,
- measuring between the resistor and diode against the outside X post will result in X+Y+R.

Let's try to establish which coil serves which purpose exactly.

Also, do you have a low voltage DC power source? Something less than a 12V battery, we'll be doing some testing, and lower voltage is better for preserving the coils. 6-9Vdc would be ideal.

Yes, exactly.

Here's how it looked like at the beginning:

Only thing that comes to mind is rigging up 4 AA batteries to amount to 6V, if that works.

I'm off to check the resistances. I'll report back when I'm done.

Ok, so as discussed earlier, there are only 3 posts that are wired, and the + post seems to have 2 wires.

X gives me 130 Ω
Y gives me 88 Ω
And linking both outposts (bypassing +) gives me 218 Ω

Ok, then we can try to low voltage test.

Below is a sketch, with X & Y coils marked. These represent your gauge coils. You'll note that I'm asking you to do something not inline with your previous reports. Should be fine with 6Vdc, but observe the motion of the needle. No diode will be used in this test, as the instrument is purely DC (from factory).

Seems to work: I find 223.

Maybe it's easier to digest in this illustration. Notice that I've swapped the GND and Float, in comparison to earlier today.

As long as needle doesn't move in the opposite direction, coils will be fine with 6Vdc. It just won't move all the way. For now, we're interested in action and direction.

OK, so in layman's terms, I need to connect the negative pole of the improvised 6V battery to a point between the resistor and the diode, and the positive to the + post, right? And see which direction the needle moves toward.

I'll be back

Test done, 6.3V tested output for the line of batteries.

Behind resistor to + post, the needle moved quickly to the left.

Behind resistor to former negative / now float: the needle moved slowly to the right.

Ok, that's not what we want. Let's go back to this then.



- let's put the makeshift battery between + post and GND, and observe the needle. If it moves slowly to the right, then
- use a jumper and connect the free end of the resistor (between the resistor and diode, if diode is still there) and GND. This should move the needle further to the right.

Good morning to you! I just checked connecting - to ground and + to the + post, and the needle rushed straight to the left.

Thanks mate 😁 Good night to you soon?

That's strange behaviour, completely unexpected. Let me digest a bit, and come up with a new plan.

It just occurred to me that the last test mirrored the "current" working setup in the speedo. Strange indeed.

I checked with + to + and - to "behind the resistor", and to the left went the needle again.