Just curious:
Do you know if the battery was used to heat the engine block or if this circuit was used to heat the battery if the engine block heater was connected?

 

24VDC in from optional engine block heater. When engine block heater was plugged into AC, it would use an included AC-DC converter to send 24V to that plug. The car would heat/charge the battery based on some criteria.

The connector is present on all models, but it is only relevant on the 05-08 models with the jump starter.

 

Cool. I'm going to have to jump start my 2009... looking for a clean way to leave a jump start cable in place and that connector location is perfect and on the booster side if I'm correct.
It's just the wrong sex and not really a high voltage terminal. If I were able to get a high voltage panel connector it would be better.

 

install power supply with diodes attached to vestigial connectors in the place formerly occupied by the jump starter. Fish an AC power cable out through a drilled hole and sealed with a grommet.

 

For those looking for a storage case for your charger, this works really well for $18. It's a link to Amazon, I have no connection to the product or seller(s).