Aviation Maintenance

Short Circuit

Another one for the books. This snag started with a poor description by the pilot, why am I not surprised, about a blown circuit breaker. I wasted a good 20 minutes chasing the wrong thing because the pilot can’t read. Although I should have caught on sooner, eventually I figured out where I should actually be looking. The cockpit flood light panel…can you spot the problem?


The positive wire to the rheostat had come loose and was grounding out on the speaker frame. This was causing the CB to pop. Yet another case of a lazy person before me who DIDN’T install the rheostat correctly and could have caused an in flight fire because:

  1. The green mounting plate was not glued to the panel, and thus able to spin
  2. Rheostat mounting nut was loose and able to spin with the plate, thus pulling on the wires
  3. All three wires had a cold solder joint, which frayed and let go
  4. None of the wires were insulated

The remedy (bottom right) only took me about 10 minutes to complete.

  1. Apply adhesive to mounting plate and install in correct direction
  2. Securely tighten the Rheostat mounting nut
  3. Clip, strip, and re-solder all three wires correctly
  4. Install heat-shrink insulation to protect the solder joints

Function check operating normally.