Date: 201404
Local time of day: 0001-0600
Location: ZZZ.TRACON, US
Aircraft: B737-400
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Electrical Wiring & Connectors
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During climb both pilots could smell burning electrical insulation. I looked across the cockpit at the First Officer when I noticed smoke rising from the left side of the First Officer's yoke. The First Officer was unable to see the smoke seeping through his fingers. The smoke was so thin that I could only see it when the sun shined on it. First Officer noticed the left hand grip of his yoke was hot. We determined the smoke was coming from the lighted numerical thumb wheel installed on the yoke. We turned off all the instrument lighting in the cockpit and began the SMOKE; FIRE; OR FUMES IN PASSENGER CABIN OR FLIGHT DECK Checklist. Before reaching the step for BUS TRANSFER Switch OFF the smoke and fumes had dissipated. The grip on the yoke was not as hot as when we first saw the smoke. We elected to discontinue the checklist since it appeared we had isolated the source and the smoke and fumes had dissipated. By this time; we were overhead ZZZ1 at 15;000 feet. We decided not to continue the flight and after consulting with Dispatch; we diverted to ZZZ1. Performed normal descent and approach checklists to an uneventful landing. Because of the close proximity of the airport we did not take time to identify and pull circuit breakers. Did not exceed landing weight limitations. Maintenance revealed the light assembly in the yoke had failed; shorted; caused smoke and fumes; and the hot grip on the First Officer's yoke.


Second narrative: On climb out; we were in a right turn back to the VOR when the Captain and I both smelled a 'burnt electrical' smell. Captain then said he saw whisp of smoke coming from my yoke thumb wheel. Initially I couldn't see the smoke since I was looking into the sun; when we rolled out on heading I then saw the smoke as well. We started the Smoke/Fumes Checklist and turned off all lighting rheostats. The smoke stopped but we still had the burning smell. We stopped the checklist short of isolating electrical buses since we were confident of the cause. We then coordinated a divert. The Captain decided not to declare an emergency since the smoke and smell had gone. We landed uneventfully and debriefed passengers and crew.


Synopsis: B737-400 flight crew detects smoke during climbout and isolates it to the First Officer's left yoke hand grip which is hot. All instrument lighting is turned off and the yoke begins to cool. Crew elects to divert to a suitable airport.