You can do your own load test if you have a volt meter and someone to crank the starter while you watch the voltage drop, disconnect coil for test.
Get a volt meter and test voltages at the alternator
But first measure battery voltage, 12.7v for new battery, and then start engine
After starting voltage at battery should read 14.5v or higher, and then drop down to 13.6v after a few minutes.
If you just get the 12.7v after starting then alternator is not "on"
Test voltages on the alternator with key OFF
B+, black/orange stripe wire, should have battery voltage, 12.7v
A, yellow/white stripe wire should also have 12.7v
If either has low or no volts then you have a bad fusible link or wire
Then Key ON
The light green/red stripe wire is the "on" switch for the alternator, see diagram below
This is the charging circuit for 2003 Ranger