How To Test The Headlight Switch (1994, 1995, 1996, 1997 Chevy S10 And GMC Sonoma)

This tutorial will explain how to test the headlight switch on your 1994, 1995, 1996, and 1997 Chevrolet S10 (GMC Sonoma).

We'll test the headlamp and park-lamp circuits of the headlight switch.

When the headlight switch fails, the headlights won't come on.

NOTE: This tutorial applies to both the 2.2L and 4.3L equipped S10 and Sonoma (1994-1997), since they all use the same headlight switch.

You can find this tutorial in Spanish here: Cómo Prober El Interruptor De Las Luces Delanteras (1994-1997 2.2L Chevy S10) (at: autotecnico-online.com).

Headlight Switch Basics

How To Test The Headlight Switch (1994, 1995, 1996, 1997 Chevy S10 And GMC Sonoma)

The headlight switch is a simple on/off switch that can be easily tested with a multimeter and by bypassing it (with a jumper wire).

Although the headlight switch has 6 male spade terminals, its connector has wires for only 4 of them.

When it fails, you'll see a ‘no headlights’ and/or ‘no park-lights’ condition.

TEST 1: Testing The Continuity Of The Headlight Switch

To get our headlight switch diagnostic under way, we're gonna' test the continuity of the headlights and park-lights circuits (inside the switch) with a multimeter.

The two park-light switch terminals that we're gonna' test are male spade terminals A and E.

The two headlight switch terminals that we're gonna' test are male spade terminals C and D.

The illustrations in the image viewer above will help you identify them.

Let's get started:

  1. 1

    Remove the headlight switch and place your multimeter in Ohms mode.

  2. 2

    With the park-lights switch in its OFF position your multimeter should read NO continuity on male terminals A and E.

    Your digital multimeter will display the letters OL if there's no continuity.

  3. 3

    With the headlight switch in its OFF position your multimeter should read NO continuity on male terminals C and D.

    Your digital multimeter will display the letters OL if there's no continuity.

  4. 4

    With the park-lights switch in its ON position your multimeter should read continuity on male terminals A and E.

    Continuity means any resistance value that is not the letters OL on your multimeter's display. The known-good headlight switches I've tested have given an Ohms reading between 1 mega-Ohm to 500 Ohms when continuity is present.

  5. 5

    With the headlight switch in its ON position your multimeter should read continuity on male terminals C and D.

    Continuity means any resistance value that is not the letter OL on your multimeter's display. The known-good headlight switches I've tested have given an Ohms reading between 1 mega-Ohm to 500 Ohms when continuity is present.

Let's analyze your multimeter continuity test result:

CASE 1: Continuity exists in the indicated terminals when you turn “on” the headlight switch. This is the correct and expected test result.

For the most part, a continuity reading tells you that the headlight switch IS NOT defective. But to be sure, I recommend going on to the next test: TEST 2: Bypassing The Headlight Switch.

CASE 2: Continuity DOES NOT exist in the indicated terminals when you turn “on” the headlight switch. This test result almost always means that the headlight switch is defective.

To be sure, I suggest doing one more test and it's to bypass the switch itself. For this test go to: TEST 2: Bypassing The Headlight Switch.