How To Test The Turn Signal Switch (Step by Step)

TEST 3: Flasher Voltage Input

IMPORTANT: If you haven't already disabled the air bag system, do so now. You can find the instructions here: Disabling the Air Bag System (SIR).

You've reached this point because TEST 1 and TEST 2 have confirmed that the turn signal switch is getting power and is re-routing this power (voltage) to the turn signal flasher.

Now, once the flasher gets this voltage (from the turn signal switch), it re-routes it back to the turn signal switch but this time this voltage will be under the control of the flasher to make the turn signal lamps blink ON and OFF.

The circuit (wire) that you'll be checking in this test is the one labeled with the number 9 of the Gray turn signal switch connector.

IMPORTANT: You won't be probing the front of the disconnected connector since all of the turn signal switch's connectors have to remain connected to the instrument panel harness connector for these tests to work. What you'll do is probe the wire (with a wire piercing probe or similar tool) somewhere between the turn signal switch and the specific connector the test instructions call for.

OK, this is what you'll need to do:

1. Identify the circuit labeled with the number 9 of the gray connector.
   • The gray connector must remain connected to the instrument panel harness connector at all times during this test.
2. Turn the ignition switch to the ON position.
3. With your multimeter to Volts DC mode:
   • Probe the wire that corresponds to the number 9 with the red multimeter test lead.
4. Ground the black multimeter test lead on a good Ground point.
5. The multimeter should read 10 to 12 Volts DC.

Let's examine your test results:

CASE 1: Your multimeter registered voltage (10 to 12 Volts). This is the normal and expected test result, go to: TEST 4: Front Right Turn Signal Output.

CASE 2: Your multimeter DID NOT register voltage (10 to 12 Volts). Re-check all of your multimeter connections and repeat the test one more time.

If your multimeter still did not register any voltage, then one of two things are happening:

1. The flasher is bad and needs to replaced.
2. An open-circuit problem in the wiring between the flasher and the turn signal switch connector (although this is very rare).

I recommend that you replace the flasher and re-test. Testing for an open-circuit problem between the flasher and the turn signal switch is beyond the scope of this article but you have at the least eliminated the turn signal switch.

TEST 4: Front Right Turn Signal Output

IMPORTANT: If you haven't already disabled the air bag system, do so now. You can find the instructions here: Disabling the Air Bag System (SIR).

OK, all of the basic test are out of the way (TEST 1, 2, and 3), it's time to check the actual turn signal switch output to the turn signal lamps.

We're gonna' start by testing the Front Right turn signal output to the turn signal lamps in the front of your GM pickup, SUV, or van.

NOTE: You don't have to start here. You can start at any of the tests that apply to your specific situation. If you don't know where to start, then I suggest that this be your starting point.

The circuit that you'll be testing (in this test step) is the one labeled with the number 6 of the Black turn signal switch connector.

OK, this is what you'll need to do:

1. Identify the circuit labeled with the number 6 of the black connector.
   • To identify the wire you need to test, you'll need to disconnect the turn signal switches connectors from the instrument panel harness connector.
   • The black connector must remain connected to the instrument panel harness connector at all times during this test.
2. Turn the ignition switch to the ON position.
3. Once again, your multimeter must be set to Volts DC mode:
   • Probe the wire that corresponds to the number 6 with the red multimeter test lead.
   • Probe the wire somewhere between the black connector and the turn signal switch using an appropriate tool (like a Wire Piercing Probe).
4. Ground the black multimeter test lead on a good Ground point.
5. Activate the Right Hand turn signal lamps
6. You're gonna' see one of the following test results:
   • A battery voltage (10 to 12 Volts) that flashes ON and OFF.
   • No battery voltage at all.
7. When done, turn off the turn signal switch and the ignition switch.

Let's examine your test results:

CASE 1: Your multimeter registered voltage (10 to 12 Volts) flashing ON and OFF. This is the normal and expected test result and tells you that the turn signal switch is activating the Front Right turn signal lamps.

The next step is to check the Rear Right turn signal lamps output, for this go to: TEST 5: Rear Right Turn Signal Output.

CASE 2: Your multimeter DID NOT register voltage (10 to 12 Volts) at all. Re-check all of your multimeter connections and repeat the test one more time.

If still NO voltage, then the turn signal switch is bad (internally) and needs to be replaced.