If the wire length is between the battery and the power supply, add a 1,000uF capacitor AND 100nF capacitor in parallel across the input (battery) side of the power supply at the power supply end. If the wire is between the power supply and the controller circuit, add 100nF and I would suggest 10uF in parallel close to the controller.
It sounds like either you are drawing enough current to cause a voltage drop in the wires or their impedance is high enough to make the power supply unstable. The capcaitor will help to fix that.
Brian.