T
The Ghost
Personally I would have gone around to assay the problem, could have been future work. But I am like that! As you say your contract applied to supplied parts only and you did not supply the lights. Further the contract as you say was between you and another party. The new owner has no privity with that contract and cannot therefore rely upon it. In order for a contract to be valid there must be something of value exchanged like you did the work and the lady paid the money. I would have rather said what I would and would not do face to face. But then as you say if the alarm was ringing for nightmare customer, as you were then!