The hum doesn't come from the instrument, really, it's coming from the environment, but is picked up by the guitar pick-ups, then amplified. The Gibson (and maybe the other, successful...) guitars have 'humbucking' pick-ups; that term tells us something. Their pick-ups have been so designed and made to pick up hum twice (with double coils...), then cleverly have one of these signals cancel out the other. The hum you cured was picked up, not by the pick-up, but from the cabling and switch stuff which, once shielded, picked up the hum no more.
The Tele, on the other hand, has single -coil pick-ups, designed and made precisely to pick up electrical signals from the magnetic field around the strings, but also any other stray hum, without distinction, nor this clever method of cancelling. That's why shielding, so efficient on the other guitars, won't help the Tele, unless you shield the pick-ups, in which case they won't pick up the strings..!
Two solutions, really. The first is to swap out the Tele pick-ups for single-coil-shaped humbuckers. You'll lose the hum, but will no longer have that delicious 'Tele' twang, and they're not cheap.
The other is to track down the source of the hum (electrical fittings such as halogen or neon lighting, or light dimmer switches, some transformers... The list is long...). This can sometimes be aided by stalking around with the guitar, offering it up to all points in the room, trying to find where the hum is loudest. Not always easy, nor successful. We have a six-string bass with 'J'-type pick-ups (and so single-coil...) which picks up hum when too close to the bass amp (a valve Hiwatt, so huge transformers...). Turning the amp off cures the hum, but leaves the bass with much lower volume..! D'oh..!
Hope this helps.
