Cheapest and easiest way to slow down a motor

[KenWittlief]

if you put two motors in series they will have half the power (run at 6V). This is only true if they are equally loaded. If one motor is loaded more that the other it will slow way down or stop, then the other motor will run at full speed.

A simple way to make a chopper circuit is to get a 12V SPDT relay, and put the relay coil in series with the normally closed contacts. When you energize the relay the contacts will open, causing the relay to close again... and you end up with a buzzer. The other pair of contacts can then be used to power the motor, chopping the power, very much like a Victor speed controller.

I cant venture a guess whats in the box. If it runs on DC then it cant be SCRs or Triacs, because they depend on AC to be able to unlatch. There is no duty cycle for an SCR or Triac to chop with a DC power source.

The light bulb will work. Try a normal 110V 100 watt lamp. That way you wont have to worry about the heat dissapation: the bulb will glow dimly. If a 100W lamp lets the motor run too fast, switch to 50W or 25.