While taxiing a Lear 35, the crew reported an intermittent Nose Wheel System (NWS) squawk that would not allow them to make wide turns or corrections while steering. Instead, the NWS operated as if the aircraft were moving at a high rate of speed, essentially not allowing any steering movement at all.
With phone support from Duncan Aviation technicians, the customer replaced the computer, servo and rang out the cables. Proper low-speed operation was restored after they disconnected the P227 connecter at the nose wheel steering computer. The wheel transducers are generators that communicate the aircraft's speed to the computer through the P227 connection. The wiring was checked and one suspect transducer was replaced but still had no affect on the issue.
While removing power to various ancillary systems in the aircraft, the NWS returned to normal operation when the copilot's instrument lighting was disabled. Replacement of the copilot's lamp dimmer box (located in close proximity to the NWS computer) corrected the issue. It is suspected that the lamp dimmer box, which otherwise functioned normally, was transmitting radio frequencies picked up by the wheel transducer cable causing the NWS computer to malfunction and perceive the aircraft was moving at a high rate of speed.
