Originally Posted by Sandra L
I do not know if I have this cut-off feature on my 2005 Sienna w/tow package. Will I need to contact Toyota to find out?
Toyota does not offer pre-wiring for any trailer feature on the Sienna (lights, brake control, or battery charging). The factory-installed "towing preparation package" is all durability features (mostly transmission cooling on the 2005), while dealer-installed (or port-installed) accessories include a hitch and a trailer lights wiring package. The wiring package doesn't have any brake control or battery-charging features at all, so if you have either of those they were a custom installation - Toyota won't know anything about any custom installation which may have been done.
My 2004 Sienna's trailer lights wiring package is the dealer-installed accessory. I added trailer brake control and trailer battery charge wiring myself, and I did include an isolation (cut-off) relay so the van and trailer batteries are only connected when the van's engine is running.