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Home > Video > Video Display > How to test an Alternator (not charging from a blown fuse) - Mazda

How to test an Alternator (not charging from a blown fuse) - Mazda

This video covers the basic procedures needed to check an alternator that’s not charging, as well as some in-depth insight into the field control circuits. The bulb circuit bypass test shown is particularly valuable to learn, and applies to many other alternator designs, not just Mazda. Be sure to check out Part 2 for the follow up to this video, and some lessons on short to ground testing!

Engine Performance Diagnostics chapter 1

  - dead battery
  - inoperative dash lights/gauges
  - stall
  - engine won’t crank

  - replace the blown fuse (short found in Part 2)

Tests shown
  - using a wiring diagram to dissect an alternator control system
  - how to check for charging voltage at the alternator
  - using voltage drop to check the alternator B+ circuit
  - understanding how a discharging battery can skew your readings
  - checking the field control circuits, including the bulb circuit
  - how to perform a bypass test with an incandescent test light
  - using the key on bulb check to identify a bulb problem
  - how to check fuses with a test light
  - using voltage drop to check the alternator ground
  - understanding how the alternator regulator controls the cluster bulb
  - incandescent vs. LED test lights

Tools used
  - ATD Tools 5519 Auto Ranging Digital Multimeter with Protective Holster
  - OTC 3633 Mini Circuit Tester

  - (Chapter 1) Misfire ID, Compression Tests, Vacuum Leaks, Fuel Trim, Head Gasket, Restricted Exhaust, Low Power, DMM

Related videos
  - Fuse keeps blowing (how to locate a short to ground) - Mazda
  - Bad Alternator Diode causing transmission/speedometer problems
  - How to test an alternator (Chrysler Dodge Jeep)
  - Battery keeps going dead (what to test before replacing)
  - How to measure the current draw of your test light (Incandescent vs. LED)

For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available at  as an eBook or paper book.
Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium https:// There is a 14 day free trial. 
On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!

Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information.  ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video.  Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result.  Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC.
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