Installing Regent with belt in 2003 Windstar

For the life of me I can't remember if I'm in a 2002 or 2003, but hopefully it doesn't matter. It has captain's chairs for the second row.

We're getting the Regent as my son's next carseat and I thought I remember reading that LATCH can't be used over 48lbs. That's not within the near future for us, but I thought I'd see about the belt installation on my vehicle for reference. I can't seem to get the shoulder belts to lock by pulling it all the way out and letting the tension go. The manual to my vehicle mentions nothing about locking the belt. The directions basically say to thread the belt through the seat, pull out the slack and you're done. I haven't actually tried locking the seat in. I haven't bothered since I can't get the shoulder belt to lock up.

So my question is, assuming I can't figure out how to lock the belt or find that it does lock but isn't consistent, is this where I'd use a locking clip? Will one come with my seat or will it need to be ordered along with it? I've always used LATCH before so I'm pretty clueless.

[scatterbunny]

I have a 99 Windstar, which is essentially the same, no lower anchors, though (top tethers in all positions, though!).

I have a Husky (same as Regent) in the driver's side captain's chair. The belts lock at the latchplate, not at the retractor. The shoulderbelt porition will remain loose until a sudden stop or crash. The lapbelt portion is what holds the carseat tight. All you have to do is thread the belt through the belt path (I prefer the long belt path) and pull the slack out. Sometimes I have to unbuckle after I pull all the slack out, tighten the belt up a smidge more and then bounce on the seat to re-buckle. Reclining the vehicle seat a notch or two while you are installing and then pulling the vehicle seat back upright after installing really helps create that rock-solid feeling.

HTH!