How to Test the Low-High Beam Headlight Dimmer Switch

This article will help you to test the Low-High Beam Headlight Dimmer switch on your GM pick up, van, mini-van or SUV.

Specifically, you'll be able to troubleshoot and diagnose a No Low Beams or a No High Beams Headlight problem.

As you might already be aware this Low-High Beam Headlight Dimmer Switch is part of the Turn Signal Switch.

In this article, I'll show exactly what you need to do to test it. Now, if you need to just test the Headlight Switch, you can find the test article here: Headlight Switch Test.

To help you navigate this article, here are its main points:

  1. Symptoms of a BAD Low-High Beam Headlight Dimmer Switch..
  2. What Tools Do I Need To Test The Headlight Switch?
  3. Circuit Descriptions.
  4. TEST 1: Checking Headlight Switch Input.
  5. TEST 2: Low Beam Headlight Output.
  6. TEST 3: High Beam Headlight Output.
  7. Test Summary.

Symptoms of a BAD Low-High Beam Headlight Dimmer Switch

The most common (and well, probably the only one) is usually the low beam headlights don't work.

In my personal experience, when the Low-High Beam Headlight Dimmer Switch has failed, you'll only be able to roll around using the high beams only.

Well, in this article, I'll show you how to test it in a step-by-step way. You'll be able to say that Low-Beam Headlight Dimmer Switch is indeed BAD or that it's not.

What Tools do I Need to Test
the Low-High Beam Headlight Dimmer Switch?

You'll need some basic hand tools to remove the Steering Wheel covers and some of the dash panels, to access the Low-High Beam Headlight Dimmer Switch wires.

You'll also need:

  1. Multimeter.
    1. The multimeter can either be a digital one or an analog one.
    2. If you need to upgrade or buy a multimeter, check out my recommendation: Buying a Digital Multimeter for Automotive Diagnostic Testing (found at: easyautodiagnostics.com).
  2. Wire Piercing Probe.
    1. Although this tool is not an absolute must, if you do buy one, you'll realize just how easy it makes testing the voltages inside the wires.
    2. If you need to see what this tool looks like, you can see it here: Wire Piercing Probe.

As you can see from the list above, it's nothing that's gonna' break the bank.

Circuit Descriptions

How to Test the Low-High Beam Headlight Dimmer Switch

As mentioned at the beginning of the article, the Low-High Beam Headlight Dimmer Switch is part of the Turn Signal Assembly.

If you have already taking the steering column covers off, you've noticed that the turn signal switch has a lot of wires connecting to it.

All of these wires connect to one of two connectors. One connector is a Gray one and the other is Black.

Luckily, we only have to worry about testing 3 wires.. and these three wires are the ones that are part of the Gray connector (see image 1 of 3)

If you disconnect the Gray connector from the instrument panel harness... you'll notice that the Gray connector has the numbers 1 through 13 embossed on one side (see image 2 and 3).

The three wires that we need to worry about, are the ones that connect to pins 11, 12 and 13 of the Gray connector.

Here are the circuit descriptions:

  1. Circuit 11: High Beam Headlight Feed.
  2. Circuit 12: Low Beam Headlight Feed.
  3. Circuit 13: Input from Headlight Switch.

You'll notice that there's no mention of the colors of the wires... and this is intentional, since the colors on your specific vehicle may be different.

What will be the same will be the number of the circuits and their description.

Alright, let's turn the page and get testing...