With the two batteries side by side connect a jumper wire from the positive post on one battery to the negative post on the other. The remaining neg and pos posts on each battery will supply the 24V your looking for.
Cut the blue wire that goes into the actual motor
to wire the license plate lights you must have lights and wire them to the scooter.
Isolate the wire going into kill switch [wrap some tape round it] so it cannot be earthed.
for automotive purposes, you will need two 12 volts batteries connected in SERIES. That is, connect the two batteries with one cable from positive to negative. That will give you 24 volts. In order to charge both batteries with one alternator, you will need a battery equalizer
You do not need three 12 volt batteries to get 24 volts, all you need is two batteries. So I assume by using three batteries you want to increase the amperage. Wire two of the batteries in series and then wire the third battery to the second battery in parallel and you will have 24 bolts. Or you can just wire two 12 V batteries in series to get 24 V.
step up trasnsformer <<>> As suggested above transformers do not work on DC installations. You will need to use two 12 VDC batteries in series with each other to obtain the 24 VDC needed to operate the motor. Connect a jumper between the two batteries with a wire the same size as the wire coming from the motor. The jumper will go from the negative of one battery to the positive of the second battery. The two remaining posts will connect to the motor and have a potential of 24 VDC.
No they do not. They have batteries in them, but the batteries are not replaceable. Information from ChaCha.com
That depends on what voltage your batteries are,
Positive wire is red, at least on automobile batteries.
Selection of enameled wire for motor
Perhaps ground wire to Kill engine
If the motor is operated from a three phase three wire distribution system the motor will not need a neutral wire.