The absolute best tester for testing electrical components on our "older" vehicles is the Sunpro CP9080. Very inexpensive, and reliable. Been using mine for over 20 years. It is no longer made, but they show up on e-bay from time to time. Sunpro CP9080 Sensor Tester Plus For Engine Sensors and Ignition Modules - Black | eBay
EDIT: If you buy one, make sure it has the manual