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Here's my guess.
It's a long powercord not attached to anything.
One end just happens to be stuck down under that seat.
You didnt even raise the seat and see where it goes before posting on the Forum?
Its been 11 days and you still haven't?

I'm a Fart Smeller. LOL
probably for powering LED lighting
https://www.ledunderbody.com/cigarette-lighter-power-adapter/
$50 says you have some fancy LED mood lighting on your new Expo and don't know it
probably inside the vehickel since cord is clean. If there is a hole through the jack storage area to the underside of the Expo, the LED lightbar or flux capacitor may be mounted there?
thanks for following up!
update .... I'm still bored
or it might be a fuse tester? if you plug the blue & white terminals into each other and plug the other end into the power port ... you'll find out if the fuse works. Not advised though.

my badKnowing it was a former police vehicle would have probably ended this days ago. Lol.
EXACTLY!!!Knowing it was a former police vehicle would have probably ended this days ago. Lol.

I’m going with flux capacitor cord.
Me???? I’m a legend in my own mind my friend. The older I get, the better I was! Ok I stole those lines from my “Old Guy’s Rule” shirt. But you know there is some truth there...Lol!Who are you who is so wise in the ways of science?