Modern Vespa

A few weeks ago, started getting an occassional single horn toot immediately upon starting the engine. Today, while standing in traffic with the tilt-lock on, horn started blaring - very embarrassing.

Pulled the nosewear and confirmed that the hydraulic resevoir was full. I had already researched the various threads and knew that the next most likely culprit is a bad sensor, like practically everything else odd that happens with the MP3's electrical system.

I think I spotted the sensor itself, but I have a question that AFAIK has only been asked once in all the threads on this topic, and never answered. Knowing that my hydraulic system is in fact actually working; realizing that what I propose could mean that in the future I could have a bad tilt-lock system and not know it; and appreciating that the worst thing that could happen would be that the bike could conceivably fall over while stopped (but having zero impact on the safety of the bike while moving)...

...is it possible to simply disconnect or bypass the sensor (or even better, pull a fuse [edit: or a relay (thanks jim)]) so that the hydraulic alarm stops activating, but without affecting any other system in the bike?

Yes, I know that the best thing, the smart thing, the right thing is to replace the sensor. I'm asking, is that the only thing?

P.S. I have discovered that there is one small compensation for changing back to the stock variator from the J. Costa: the shudder it gives off between 1500 and 2000 RPM is in exact harmony with my topcase, and the entire topcase vibrates madly as I accelerate, sounding like I have a much larger engine and aggressive exhaust. At least, I'm telling myself that's an advantage.

You can eliminate the horn tilt-lock warning by removing the horn warning relay.

It's the one with white and blue/black control wires, and yellow/pink and yellow/red contact wires.

This will not affect the normal manual horn operation.


Best to mend the sensor though.

Thanks Jim. I'll be disconnecting that relay while I drink a cup of coffee pondering the sensor question.

The pressure sensor is just an on/off switch so should be easily checked using a meter pressurised/unpressurised.
The horn going off could simply indicate air in the system or worn seals in the cylinder.
I would be tempted to try bleeding it at the two bleed nipples on top of the front shocks.
Put it on the stand and lock the system a couple of times.
Then just quickly crack open each bleed nipple in turn operating the lock between each one.
Don't open the nipples for long just crack them open quickly and close.
Cover the brakes with a cloth as fluid can drip on them

Thanks gilburton, I seem to have accidentally misplaced the relay I removed by complete accident and since that has fixed my immediate problem, I am all set to go until I accidentally find that relay that I completely accidentally lost by accident.

If I sell the bike, I think I might still be able to find it. I may have accidentially put it with the other stuff I've accidentally removed over the years.

I suspect that if parked on level ground the loss of hydraulic pressure would not immediately make the MP3 fall over. The main tilt mechanism would still be locked. However if it was pushed it probably would go over quite easily.

The great benefit of being able to park upright on uneven ground would be lost though and it would be dangerous to stop and start with feet up as some riders do.

All theory though - has anyone tried it?

regards Roadster

If gilburton is right and you have air in the system or a worn seal rather than a bad sensor, then removing the horn relay is probably not the best fix.

It's isn't meant to be a fix - just a work-around until it can be fixed. It's not a safety-critical component after all.