The motherboard probably has the connector. On other Dell laptops I've opened, even those without a backlit keyboard had the connector present on the motherboard (if backlit keyboard was an option for that model, which it was for yours).  So, yes, you probably can install the backlit keyboard if you can find the one that was intended for your model. It appears as though you will have to replace the entire palmrest and keyboard, as they are part of a single assembly and part number.
I have a Dell Inspiron 15 3511 with a non-backlit keyboard. Am I able to replace the keyboard with a backlit one?The community says that in order to have the backlit keyboard work, the motherboard should have a separate cable port for lightening so I am not sure how to check it without opening the laptop case.
Inspiron 15 3511 backlit keyboard