Not sure what all this talk about sense lines is about. There are no sense lines in the new electronic switches.
In the old days when using diodes, they had a sense line back to the alternator to compensate for the diode drop. Otherwise the alternator voltage was too low.
Isolator solenoids shouldn't get too hot. They only consume power to keep the solenoid energized. The contact resistance should be low. If it's not, then the solenoid needs replacement. The problem is that cheap solenoids are originally installed. They will fail! You can replace them with silver contact solenoids and they will last for a long time.
Sal