How To Test The Headlight Switch (GM 1990-1994)

In this article I'll show you how to test the headlight switch, on your Chevrolet or GMC pickup or SUV, with a multimeter.

You'll be able to troubleshoot a 'no headlights' and/or a 'no parklights' condition and decisively say that the headlight switch is bad or not the cause of the 'no headlights' or 'no parklights' problem.

To help you make sure this article applies to your specific Chevrolet or GMC pickup or SUV, this article will help you test the following headlight switch part #'s:

• AutoZone Duralast Part # SW932.
• AC Delco Part # D1561D.
• AirTex, Wells Part # 1S4760.
• Standard Motor Products Part # DS647T.
• Standard Motor Products Part # DS647.
• OEM (Original Engine Management) Part # HLS24.
• Wells Part # SW932.

If this headlight switch tutorial does not apply to your GM pickup or SUV, there's one more headlight switch tutorial for 1995 or newer GM pickups that you can find here: How To Test The Headlight Switch (4.3L, 5.0L, 5.7L).

Symptoms Of A Bad Headlight Switch

The most common and the most obvious symptom of a bad headlight switch is that the headlights (headlamps) don't come on when you turn the headlight switch on. You'll also see:

• No park lights.
• No instrument cluster illumination.

The headlight switch test itself is a pretty simple and straightforward affair and in this article, you'll find the step-by-step testing instructions you'll need to troubleshoot a bad headlight switch.

What Tools Do I Need To Test The Headlight Switch?

Here's a basic list of tools you'll need:

1. Multimeter.
   • The multimeter can either be a digital one or an analog one.
   • 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. A jumper wire.
   • Ideally, this jumper wire should have an inline fuse attached to it.
   • Now, a fused jumper is not necessary since you can use a regular wire as a jumper wire.
3. Wire piercing probe.
   • 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.
   • If you need to see what this tool looks like, you can see it here: Wire Piercing Probe.

You'll need basic hand tools to remove the headlight switch from the instrument panel (to gain access to the wires).

Where To Buy The Headlight Switch And Save

You can find the headlight switch in any auto parts store. If you're wanting the buy the original AC Delco headlight switch, you can buy it online for a whole lot cheaper than somewhere local.

The following links will help you comparison shop for the AC Delco and after market headlight switches:

Will the above headlight switch fit your particular GM pickup? Don't worry, once you get to the site they'll make sure it fits (by asking you the specifics of your particular vehicle). If it doesn't fit, they'll find you the right one.

Circuit Descriptions Of The Headlight Switch Connector

The headlight switch connector has 7 slots. 2 of those 7 are empty.

In the photo of the connector above, you'll notice that I'm using letters to identify the circuits.

If you take a close look at the bottom of the headlight connector, you'll notice these letters embossed on it.

Throughout the article, I'll be using these exact same letters to aid you in identifying the circuits that you need to test.

These are the circuit descriptions of the headlight and dimmer switch

Headlight Switch Connector Pin Outs
Pin	Wire Color	Description
A	Brown	Park Lights, Tail Lights, Radio Illumination, A/C Control Illumination, Convenience Center Illumination
B	--	Empty
C	Red	Battery Voltage Fused Feed
D	Yellow	Headlight Feed Output
E	Orange	Park Lamps Battery Fused Feed
F	--	Empty

TEST 1: Headlight Battery Power Circuit

The very first thing you and I need to do, is to make sure that the headlight switch is getting power.

This power comes in the form of battery voltage (which will range between 10 to 12 Volts DC) from a fusible link in the Junction Block (in the engine compartment).

In this test step, we'll check that the headlight circuit is getting battery power. In TEST 2 we'll check that the park lamp circuit is being fed with battery power.

You can test for power several ways. Here a few suggestions that may save you a headache:

• You can probe the front to the connector, but be careful since inserting anything into the front of the connector's female terminal, like the multimeter's lead, can permanently open it and thus damage it.
• It's best to back probe the connector or use a wire piercing probe instead of probing the front of the headlight switch connector.

OK, to get the troubleshooting started, this is what you'll need to do:

1. 1

   Remove and unplug the headlight switch from its electrical connector.
   
   Set your multimeter set to Volts DC mode.

2. 2

   Probe the wire that corresponds to the circuit C (see photo in image viewer) with the red multimeter test lead.
   
   NOTE: You should test this circuit by either back probing the connector or using a Wire Piercing Probe (the method I use). Or gently touching the multimeter probe to the front of the connector.

3. 3

   Connect the black multimeter test lead to Ground.
   
   NOTE: It may be a bit hard to find a good Grounding point inside your pickup, so what I suggest you do is to use a battery jumper cable to Ground the multimeter test lead directly to the battery negative (-) terminal.

4. 4

   Your multimeter should register battery voltage.
   
   This circuit is hot (voltage present) all of the time, whether the key is On or not.

Let's take a look at what your multimeter test results mean:

CASE 1: The multimeter registered 10 to 12 Volts. So far so good, since this tells you that the headlight switch is getting power to feed the headlight's circuit.

If you have a 'no headlights' condition but the park lights do come on, the next test should be test the headlight circuit inside the headlight switch. For this test, go to: TEST 3: Checking Headlight Circuit.

If the above does not apply to your specific situation, the next step is to confirm that the park lamps power circuit is getting juice. Go to: TEST 2: Park Lamps Battery Power Circuit.

CASE 2: The multimeter DID NOT register 10 to 12 Volts. Re-check your connections and re-test. If your multimeter still does not register battery voltage, then you've found the reason for the 'no headlight' condition.

This test result also tells you that the headlight switch is not bad since without power in this circuit, it can not turn on the headlights.

Although it's beyond the scope of this article to troubleshoot this lack of power, you now know that you need to find out why this battery voltage is missing since this will solve the 'no headlights' problem.