VESPA 633844 IT Service Manual page 190

Injection
With the interface cable harness disconnected
from the control unit, check continuity between pin
13 and the red cable of the rpm sensor connector
and between pin 15 and the brown cable of the rpm
sensor connector
With the interface wiring disconnected from the
control unit and rpm sensor connector, check that
the red and brown cables (pin 13 - 15) are isolated
from each other and insulated from the earth.
Specific tooling
020481Y Control unit interface wiring
020331Y Digital multimeter
INJEC - 30
Vespa GTV 250 i.e.