Had two electrical smoke incidents in aircraft..first was in the PTT switch in a condor stick which shorted the second was in a DC9 after landing..first time hardly anything, next sector really noticeable ..took more than an hour to trace it as we thought it was a system connected to landing gear down lock followed by flight ground switch..turned out to be a loose contact in the landing light switch .turned on after gear selection..turned off on turning off the runway.
Had another incident with a loose contact which gave us an irregular slat indication; returned to the ramp twice and eventually a loose contact was found behind the circuit breaker panel.
Had several in cars .. one caused a fire which was in a VW camper and caused by the tow bar wiring wearing out on the road with the earth touching the indicator wire..burnt out flasher unit which then set fire to the wiring under the dashboard.
Had a few others in cars, normally due to heavy load through ignition switch; have installed relays in my Bristol to relieve loads to the electronic ignition system and the dragster fuel pump which happened to blow last week..electrical fault.
As a guess but no idea of the wiring but am guessing either a loose contact causing an intermittent arcing.
As to the CFI whinging ..had a few dim fools tell me similar 50 plus years ago and I’m still flying today - normally lack of intelligence or plain incompetence. Nowt worse than a smell of burning in an aircraft or boat.