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

This article will help you to test the turn signal switch on your GM pickup, van, mini-van or SUV in a step-by-step manner and using only a multimeter.

If you've already priced the turn signal switch... you know that this bad boy is expensive (US $150 at your AutoZone or O'reilly auto parts store). So being able to test it will save you the frustration of replacing something that not only won't solve the problem... but just made you throw your hard earned money away.

So, if you're experiencing a ‘No Turn Signal’ problem and suspect that the turn signal switch is BAD... this is the article for you. You'll be able to specifically test the following:

  1. No Front Left Turn Signals.
  2. No Rear Left Turn Signals.
  3. No Front Right Turn Signals.
  4. No Rear Right Turn Signals.

One last and very important thing... this article assumes that you have already eliminated the turn signal flasher as the cause of the problem.

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

  1. Symptoms Of A BAD Turn Signal Switch..
  2. What Tools Do I Need To Test The Turn Signal Switch?
  3. Circuit Descriptions.
  4. TEST 1: Checking The Turn Signal Fuse Input.
  5. TEST 2: Checking Flasher Voltage Output.
  6. TEST 3: Flasher Voltage Input.
  7. TEST 4: Front Right Turn Signal Output.
  8. TEST 5: Rear Right Turn Signal Output.
  9. TEST 6: Front Left Turn Signal Output.
  10. TEST 7: Rear Left Turn Signal Output.
  11. Test Summary.

Symptoms Of A BAD Turn Signal Switch

It's rare for the turn signal switch to fail... but when it does, the most obvious symptom is that either the right of left turn signal won't work.

Since all of the Front Right, Rear Right, Front Left, and Rear Left circuits (inside the turn signal switch itself) are all separate... you might see one or two of the following:

  1. Only the Front Left Turn Signals don't work.
  2. Only the Rear Left Turn Signals don't work.
  3. Only the Front Right Turn Signals don't work.
  4. Or only the Rear Right Turn Signals don't work.

Since the turn signal switch isn't cheap (at your local auto parts store expect to pay about $150 US)... it's best to test it and make sure it's really BAD. In this article, I'll show you how to test it yourself.

What Tools Do I Need To Test The Turn Signal Switch?

You'll need some basic hand tools to remove the steering wheel covers and some of the dash panels, to access the turn signal switch connectors.

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 Turn Signal Switch (Step by Step)

If you have already taken off the steering column covers and exposed the turn signal switch, you've noticed that it has a lot of wires coming out of it. In fact, there are about 23 wires coming out of the turn signal switch (depending on whether you vehicle is equipped with cruise control or not).

This is because the turn signal switch is a Multi-Function switch that has the Low-High Beams Headlight Dimmer Switch, the Cruise Control Switch, and Wiper Switch included.

All 23 of these wires connect to one of two connectors. One connector is a Gray one and the other is Black.

Thankfully, we only have to worry about testing 8 wires (of the 23). Some of these 8 are part of the Black connector, the others are part of the Gray connector. Don't worry, I'll show you exactly what you'll need to test.

One more very important thing: If you disconnect the turn signal switch's connectors, you'll notice that:

  1. The Gray connector has the numbers 1 through 13 embossed on one side.
  2. The Black connector has the numbers 1 through 17 embossed on one side.

If you take a look at photos 2 and 3 (in the image viewer above) you'll see these embossed numbers on the connectors.

Here are the circuit descriptions of the wires that we'll be testing in this test article:

  1. 13 Pin Gray Connector:
    1. Circuit 6: Rear Right Turn Signal Output.
    2. Circuit 7: Rear Left Turn Signal Output.
    3. Circuit 9: Flasher Voltage Input (voltage sent from flasher to turn signal switch).
  2. 17 Pin Black Connector:
    1. Circuit 2: Ignition Fuse Input.
    2. Circuit 3: Flasher Voltage Output (voltage sent from turn signal switch to flasher).
    3. Circuit 6: Front Right Turn Signal Output.
    4. Circuit 7: Front Left Turn Signal Output.

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.

Disabling The Air Bag System (SIR)

IMPORTANT: You will to disconnect the turn signal switch's connectors from the instrument panel harness connector... and this will require that you disable the air bag system on your GM vehicle (know as SIR).


Here are the factory instructions for disabling the air bag system:

  1. Turn the steering wheel so that the front wheels are pointing straight ahead.
  2. Turn the ignition switch to the ‘Lock’ position and remove the key.
  3. Remove the ‘AIR BAG’ fuse from the instrument panel fuse box.
  4. Remove the lower steering column filler panel and:
    1. Disconnect the Yellow 2-way SIR connector at the base of the steering column.
  5. Wait 2 full minutes so that the air bag system is completely disabled.

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