Troubleshooting Low Voltage on Vehicle Reverse Light Circuit

Updated 02/21/2018 | Published 02/20/2018

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Digital Multimeter with 42" Long Test Leads - LED Display

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Question:

backup light only shows 7 volts not 12 what is the problem. If there is a problem where would it be ?

asked by: Vince

Helpful Expert Reply:

Low voltage on your vehicle reverse light circuit could be caused by damaged wire, a short against the vehicle's frame, or corroded connections anywhere from your fuse box all the way back to the contacts for the reverse light bulb.

The best method to find the issue is to trace and test the wiring for that circuit from end to end, using a circuit tester like # PTW2993 or a multi-meter like # PT89ZR that can read DC voltage. Testing will allow you to find the point where the voltage drops and that will help you know where to closely check the condition of the wiring, especially where it might be contacting the vehicle frame.

Check for worn or cracked insulation, points in the wiring where it might touch other parts and check the contacts for the light bulb. Also check that the light's ground is solidly made to a clean bare metal surface. A bad ground could cause voltage drop.

If you do find that corrosion was the issue you can use dielectric grease like # 11755 to block water from again causing the same problem.

expert reply by: Adam R