Jan, to check the operation of the throttle you will need to use a voltmeter, and ideally the wheel should be raised off the ground and the bike secured in case the wheel suddenly starts at full speed during the testing!
There should be three wires coming from the throttle which are connected to the main harness through the Black three pin connector shown here:
First check if there is ~5V between the Red and Black wires on the Black throttle connector.
If the voltage reading is correct, check the voltage between the Black and White wires which should vary between 0.8V and 4.25 when the throttle is operated. If this voltage does not vary with the throttle movement it is probably a faulty hall sensor or a broken wire on the throttle unit.
If you do not have ~5V between the Red and Black throttle wires, try connecting the Black voltmeter probe to the battery negative connection and then check the voltages at the Black lead on the throttle connector using the Red probe. If you obtain a reading or more than 0.3V on the black wire, it is more than likely to be a poor connection somewhere along the black wire that connects to each of the connectors in series. Carefully check the security of the wires in each of the crimped connections by gently pulling them to see if a loose crimped connection can be found.
Please let us know what you find.
Alan
