Originally Posted by bvmwalker
B1877 - Drivers seat belt pretensioner
B1881 - Passenger seat belt pretensioner
These codes are fairly common with 2001+ Rangers especially 2001~2003. Each code is for high resistance in 1 of the pretensioner circuits and the cause is almost always the connectors located under the driver side seat (4-wire) and passenger side seat (2-wire).
One fix is to clean those connectors and then apply a small amount of dilectric grease to the pins before reassembly. If the code(s) come back, the connector(s) may need to be replaced. As with all electrical repairs, the negative battery cable should be removed before beginning.
It is good practice to avoid storing things under the seats because that can aggravate the problem with the connectors.