A couple of paragraphs from that document suggests to me this is an add-on function, not a standard factory fitted option?
For example -
"This product is applicable only to vehicles with 12V DC, negative grounding specifications. Do not
use in vehicles with 24V specifications. Otherwise, damage to the unit or a fire may result."
and
"Do not use this product for applications other than in-vehicle use. An electric shock or injury may
result"
and
"Never attempt to disassemble or modify the product. An accident, fire, or electric shock may
result."