First, verify the 12V battery is any good. If the scooter was discarded, there's a strong chance it had burned out, nearly useless batteries. But if at least one is o.k. (it should be able to light a car headlight bulb for at least a minute without dropping in brightness appreciably) it should easily hold up to a day of launching.
To use the Electron Beam controller, open up the case and shunt (connect) the positive and negative battery contact points with a short length of wire. Use wire with a conductor that is at least as big as the wires coming out of the controller. Use solder, don't just twist them on!
Next, cut ONE wire lead about 4 feet from the controller, peel it away from the other wire, and solder battery clips on to the two fresh ends. These will connect to your
12V battery.Finally, replace the continuity lightbulb in your controller with an LED/resistor pair. A 470 Ohm resistor paired with a bright green LED capable of handling 30mA ought to be about perfect and bright enough to see in bright sunlight.
Make sure you orient the LED properly so that when the red battery clip is on the positive terminal, and black on the negative, the LED lights. LED's are polarity- sensitive, unlike lightbulbs.
This is just one way, I'm sure there are other equally good methods.