Drilling through a Kettle lid is asking for trouble (plus unless you are HFG it looks crappy)......wires are a pain in the arse......and most of us have multiple Kettles. Oh no.....what to do?
Get one flipping thermo to rule them all! The one spot in your cooking environment that should have a steady reliable temp to go by is right at the lid vent.
So get a thermometer to pop into a vent hole. Using a grate thermometer..on a wire or not....measure the temp at grate. Now compare it to the temp at your vent. There will be a difference....remember that difference. Now all you need to do is use your thermometer at the vent and reduce that number by what you were supposed to remember. Easy peasy Lousiey.
If you have multiple Kettles going at the same time that single thermometer can be moved.