If you have kids in carseats, you've probably heard of LATCH (Lower Anchors and Tethers for CHildren). The lower anchor connectors are the parts of the carseat that hook onto the lower anchors, which are the two metal bars in (or near) the crack of the vehicle seat. The tether is the top strap on the carseat, and it hooks to the tether anchor in the vehicle for forward-facing installations. (Check your vehicle manual for details about LATCH in your vehicle.)
More than 10 years ago, when LATCH was new, most carseats harnessed to 40 pounds or less, and the carseats themselves were lightweight. The lower anchors in vehicles were designed to hold a total weight of 65 pounds, which includes the child plus the carseat. At the time, there wasn't a big need for the vehicle manufacturers or carseat manufacturers to set weight limits for the lower anchors.
Fast forward to now: Many carseats are designed with harness limits like 65, 70, 85, or even 90 pounds. The carseats are also larger and heavier. Adding up the weight of these carseats and weight of the kids who can ride in them, now the numbers can easily be above 65 pounds.
So, NHTSA (National Highway Traffic Safety Administration) made a new rule. As of February 27, 2014, if the weight of the carseat plus the maximum child weight allowed (harnessed) in the carseat exceeds 65 pounds, the carseat manufacturer must have a label stating a weight limit for the lower anchors. The lower anchor limit is listed as a child's weight, and it accounts for the weight of the carseat. If your child is above this weight limit, the carseat is still safe but needs to be installed with the seatbelt. The new rule applies to only the lower anchors, and you can continue to use the tether when you switch to the seatbelt installation.
You may be wondering how the new rule affects the vehicle manufacturers. Officially, it doesn't. Only the carseat manufacturers have new the labeling requirement. However, most vehicle manufacturers have voluntarily set the limits on their lower anchors to a combined weight (child plus carseat) of 65 pounds, so even if your carseat was made before February, your vehicle may have its own lower anchor limits. If your carseat and vehicle have different lower anchor limits, choose the smaller number.
Most vehicle manufacturers have applied the changes to all model years of their vehicles. Also, since this is not a requirement for them, this information is not likely to be mentioned in the vehicle manual.
Currently, these are the lower anchor limits for vehicles (2013 LATCH Manual, Safe Ride News):
65 lbs (child + carseat): Acura, Audi, Bentley, BMW, Buick, Cadillac, Chevrolet, Chrysler, Daewoo, Dodge, Fiat, Ford (model year 2014 and newer), Geo, GMC, Honda, Hummer, Hyundai, Jeep, Kia, Lincoln (model year 2014 and newer), Mercedes Benz, Mini, Mitsubishi, Oldsmobile, Pontiac, Porsche, Ram, Rolls Royce, Saturn, Smart, Subaru, Volkswagon
Follow carseat instructions: Coda, Ferrari, Infiniti, Jaguar, Land Rover, Lexus, Maserati, Nissan, Scion, Toyota, Volvo
48 lbs (child weight): Ford (model year 2013 and older), Lincoln (model year 2013 and older), Mercury, Saab
Not stated: Isuzu, Mazda, Suzuki, Tesla
Carseat lower anchor limits will be listed on the label for seats made 2/27/2014 or later, if this rule applies to them. Remember, the label is required only if the weight of the seat plus the max weight the harness exceeds 65 pounds, so you won't find this label on rear-facing-only infant carseats, lightweight/low-weight-limit seats, or belt-positioning boosters. Also, check the carseat manual, even if your seat was made before 2/27/2014, because some manufacturers were setting lower anchor limits before the new rule.