i was given a dead tto without sensor.
i cut it open using the same approach to cutting away your skin to find a deeply embedded splinter.. ie very slowly. and carefully. i found the battery and terminals and managed to prise off the terminal from the back of the battery. the terminals seemed to be partly covered in a non conductive clear lacquer which at first i didnt realise and wondered why the display wouldnt light up after fitting a new battery.
i made a new back or cover out of clear perspex and used the 4 existing dummy screws to secure it.
then i needed a sensor. by trial and error and put on the right path by a few posts on this thread i tried NTC thermistors and found that as i went up in resistance the temperature dropped down from reading way too high to just right at 100k. for those who have the existing sensor this isnt necessary.
i then had to attach it to a plug washer and used a copper washer terminal with a crimp attached usually for wires. i trimmed this a bit and attached the thermistor with a blob of jb weld it is now ready to go under the spark plug but needs longer wires to reach the bars.
i am waiting for some fine cable to arrive.