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.
Contents of this tutorial at a glance:
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
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.
Where To Buy The Headlight Switch
The headlight switch on the 1994-2003 Chevy S10 (GMC Sonoma) isn't expensive. The following links will help you comparison shop for it and its connector and hopefully save you a few bucks:
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
Remove the headlight switch and place your multimeter in Ohms mode.
- 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
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
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
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.
