I installed two outdoor garage lights using 14/2 MC Armorlite Cable. The lights are only 8.8 watts and have day/night sensors. I connected the wiring to a garage door opener dedicated 20 amp circuit on the ceiling. This circuit has one duplex 20 amp receptacle for the garage door opener plug. The new outdoor lights 14/2 wires are fed into that box. I now realize that the wiring is not correct. I should have used 12/2 wiring. Upon advice from a friend/electrician I replaced the 20 amp breaker with a 15 amp breaker and replaced the 20 amp receptacle with a 15 amp receptacle. Is this allowed? For safety, should I replace the wiring from the outdoor lights to the garage door receptacle with 12/2 wire? Thank you for your advice.
Based on my experience (I am not a licensed electrician), I think everything you did is OK. Key was to replace the 20 A breaker with a 15 A breaker. Only other thing you might want to do is to make a note in the circuit breaker panel to the effect that "Circuit [put the number of you circuit breaker here] feeds #14 wiring", or something similar, so that someone doesn't come along in the future and seeing 12 gauge conductors going into the circuit breaker, think they can up the breaker to 20 A.