GM-GMC: Backup lights on 2001 Sonoma ext cab, gmc sonoma, alligator clip

Question
Backup lights on my 2001 GMC Sonoma ext cab do not work.  I've replaced the bulbs and checked the fuse which seems to be okay.  I even went ahead and replaced the fuse to be on the safe side. They still don't work. Any other ideas?

Thank you

Answer
You can easily test this circuit using a standard 12 volt test light due to this being a 12 volt circuit.

Make SURE the test light works BEFORE performing the below tests.


1. Remove the backup light bulb from it's socket.

2. Apply the emergency brake.

3. Turn ON the ignition switch. Do NOT start the
  engine.

4. Put the gear shift in the REVERSE.

5. Using your test light and a metal paper clip,
  straighten out the paper clip and attach one end to the
  test light alligator clip.

6. Being VERY careful touch the tip of the test light to
  one of the inner contacts of the light bulb socket and
  touch the paper clip end to the other inner contact of
  the light bulb socket and the test light should
  illuminate.

If it does NOT illuminate:

1. Remove the test light from the bulb socket and discard
  the paper clip.

2. Attach the alligator clip of the test light to any
  metal surface of the vehile.

3. Take the tip of the test light and touch one of the
  inner contacts of the bulb socket and see if the test
  light illuminates. If it does NOT, Touch the tip of the
  test light to the other inner contact and see if the
  test light illuminates.

If the test light DOES illuminate when you touch either inner contact of the bulb socket this indicates that you have a GROUND fault being most likely where the BLACK ground wire is either corroded or loose where it is secured to the frame at the rear of the vehicle.

If the test light does NOT illuminate in any of the above test procedures, Hvae a helper wiggle the gear shift lever from the PARK position past the REVERSE position to the NEUTRAL position as you repeat the test light test as stated above and if while manipulating the gear shift lever, You get the test light to illuminate, this would indicate a loose, mis-adjusted or faulty electrical GEAR SHIFT SELECTOR SWITCH of which is usually mounted on the steering column under the dash or at the transmission selector shaft on the transmission.

Let me know.

Thomas
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