After all these years, the RTGs probably wouldn't be putting out very much power. RTGs degrade over time.

The units have been switched off for a long time, so they've been fully exposed to the lunar temperature cycles. When they were on all the time, they were better able to handle the cold lunar nights due to the heat generated from the electronics. Temperature swings can do unpleasant things like cause circuit boards to crack and solder joints to weaken.

There's an even more fundamental problem: even if they could find the software to send the command to turn the units on, would they have a computer that could run the telemetry processing software? Without that software, they'd have a hard time decommutating the telemetry stream.