You are using wrong function signature for end overlap, You have to specify something like this:
void AElectricityWall::MakeWallSolidTriggerEndOverlap(class AActor * OtherActor, class UPrimitiveComponent* OtherComp, int32 OtherBodyIndex)
/** Delegate for notification of end of overlap of a specific component */
DECLARE_DYNAMIC_MULTICAST_DELEGATE_ThreeParams( FComponentEndOverlapSignature, class AActor*, OtherActor, class UPrimitiveComponent*, OtherComp, int32, OtherBodyIndex);