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The input to the Spikes are through opto isolators on the Spike, so you have to be able to supply enough current to forward bias an LED in the isolator to get it to work. Input power must be 12 volts and the RC relay outputs (PWM style connector) is most likely 5 volts.
If you wanted to have an output that tested Spikes and Speed Controllers, I would have included two inputs that are unused on the robot. It is important when troubleshooting to test the exact path to be sure things are working. Let the controller do the signal generation.