Modern Vespa

The fuel gauge only reads half full when the tank is full.
Is there an easy way to test to see if it is the gauge that is faulty or the sending unit?

Check to see if you have faulty gauge connections, if okay then probably would look at renewing the float that would require removing the tank, while its out give it a good clean Inside. 😉👍

likely the float. there's two versions: a standard float on a "boom" (wire) with an articulating arm, and the cylinder type.

the cylinder type is more prone to failure.

each takes a different wiring connector, both fit the tank the same. the only way to test the float is to remove/drop the tank, which is about as much fun as it sounds.

back feeding the gauge is a risky proposition in that you could fry out the resistor. the gauges in these rarely go bad.

Thanks.
I am not looking forward to dropping the tank.
Maybe I can make a dipstick for checking the level.
Why couldn't it be simple like the one on my PX150.

Nothing is made simple or made to last anymore, .

When my guage doesn't work the low fuel light works independent of it. See if your low fuel light works for fill ups.

I'd say that 20~24 years is a pretty good run

the tank isn't all that bad. it's more cumbersome than anything else.

disconnect the shock, pull the HT lead, disconnect the stator wiring, pop off the fuel and vacuum lines, unclip the evap/overflow tube, pull the tail light and undo that fastener, pop off the battery plate and remove the battery & tray and pull off those fasteners.

jack the body up like you're pulling the engine, only instead the tank comes out the bottom. leave one screw holding it on so that you can get one hand under the tank to steady it as you ease it down.

you don't have to but it helps to remove the turn signals and rear fender, obviously the fairings come off.

drain it before trying to pull it. otherwise it's all wobbly bobbly.

Fair comment mate, All the best for the coming year 👍