Arduino - RoboRIO Question

[Qbot2640]

We've created an Arduino based indicator that we want to use, which gets triggered by the relay signal that is sent to a Spike. (One action is activated when the motor is run in one direction, and a different action is activated when the motor is run the other direction. A third "neutral" action runs when the motor is not engaged.)

Before installing, we measured the voltage of the red and white PWM wire leads (with respect to the black) and found them to be very close to +5v (for each direction the motor is run, respectively).

Using the 5V supply from the Arduino itself to simulate the voltage from the PWM wire signals, the program worked perfectly off the robot.

When we put the indicator on the robot, it remained in the "neutral" third action no matter what we did with the motor. When we checked the voltage again (white and red from PWM WRT black), we found it to be now only approximately 1 volt.

So I guess my questions (finally) are (1) Why does the voltage read 5 Volts when not attached, and only 1 Volt when attached...and (2) Is this normal or have we done something wrong. Then (3) If this is normal, we can use an analog input...what minimum voltage should we expect at each signal pin, so we know what to use as our "trigger" value?