How do you troubleshoot the wipers on a 1999 Ford Ranger?
On my 99 ranger when the wipers started malfunctioning I had to replace the entire switch on the column. The part is easily replaced after removing the plastic shell covering the column. The steering wheel will not need to be removed, but I think the dash panel directly under the column will need to come off first. This solved my problem of random wiper activity. I'm sure there could be other problems due to motor failure or spline stripping. If the problem began when the wipers were activated while frozen I would seek another solution.
The 1999 Ford Ranger wiper blade sizes are 18" wiper blades on both sides front. See sources and related links below for more information. Since there are over 22 different wiper arm attachments, do not buy wipers just by length only - be sure to lookup exact wiper blade part numbers by vehicle make, model and year for the brand wiper you decide to purchase. This ensures correct length AND correct attachment.