How To Test: The Headlight Switch (Ford 4.9L, 5.0L, 5.8L)

TEST 3: Jumpering The Park Lamp Circuit

The very first thing we'll do, to troubleshoot the ‘no park lamps’ issue on your Ford pick up (van or SUV) is to bypass the headlight switch and jumper terminals B2 and R of the headlight switch connector (using a jumper wire).

If the park lamps come on, then we can rule out any electrical problem between the headlight switch connector and the head lamps around your pick up (van or SUV).

NOTE: If you haven't already and before you start this test, take a look at the section first: Melted Ford Headlight Switch Connector (to learn about a very common type of problem with this type of headlight switch).

OK, this is what you need to do:

1. 1

   Using a jumper wire, jumper terminals B2 and R. Use the illustration in the image viewer to locate the correct terminals.

2. 2

   The park lamps should come on as soon as you complete jumpering the two terminals of the headlight switch's connector.
   
   NOTE: If the park lamps don't turn on, turn the key to the On position. In the majority of the vehicles covered by this tutorial, circuit B2 has power all of the time (whether the key is in the On position or not) but not all.

Let's examine your test result:

CASE 1: The park lamps turned on. So far so good, since this is the correct and expected test result. This test result also tells you that:

1. That circuit B2 is getting power (12 Volts).
2. That circuit R and everything in between the headlight switch connector and the park lamp connectors are feeding power (12 Volts) to the park lamps.

The next step is to test the continuity between pins B2 and R of the headlight switch itself. Go to: TEST 4: Testing The Continuity Of The Park Lamp Circuit.

CASE 2: The park lamps DID NOT turn on. Recheck your jumper wire connections and retest.

If, after double-checking your connections and retesting, the park lamps still don't turn on, then you've eliminated the headlight switch as the cause of the problem. You'll need to:

1. Check that circuit B2 has power (12 Volts).
2. If circuit B2 does have power, then you'll to check for an electrical open between circuit R and the park lamps.

Although testing the above is beyond the scope of this tutorial, you have at least eliminated the headlight switch as bad and know what direction your troubleshooting needs to take.

TEST 4: Testing The Continuity Of The Park Lamp Circuit

If you've reached this point, you have already verified that the park lamps do turn on when jumpering the correct headlight switch terminal connectors (TEST 3).

The next step is to check the continuity between pins B2 and R of the headlight switch itself.

If there's no continuity between this pins, when you test them with headlight switch in it's ‘park lamps on’ position, then you can confidently conclude that the headlight switch is bad and needs to be replaced.

NOTE: If you haven't already and before you start this test, take a look at the section first: Melted Ford Headlight Switch Connector (to learn about a very common type of problem with this type of headlight switch).

OK, this is what you need to do:

1. 1

   Place your multimeter in Ohms mode and pull the headlight switch knob to the ‘park lamps on’ position.

2. 2

   Test for continuity between pins B2 and R.
   
   If all is ok, your multimeter should register continuity. In layman's terms, this means any resistance value below 5 ohms or less.

3. 3

   Push the knob back in to it's ‘off’ position.
   
   Your multimeter should now show NO continuity. This is usually represented on the multimeter's screen by the letters OL.

Let's interpret your test result:

CASE 1: The multimeter registered continuity when you pulled the headlight switch knob to the ‘park lamps on’ position. This is the correct and expected test result.

This test result also tells you that the park lamps circuit inside the headlight switch is good.

CASE 2: The multimeter DID NOT register continuity when you pulled the headlight switch knob to the ‘park lamps on’ position. Recheck your multimeter connections and retest.

If, after double-checking your connections and retesting, the headlight switch still doesn't show continuity between pins B2 and R, you can confidently assume that the headlight switch is bad and needs to be replaced (even more so if in TEST 3 the park lamps came on when you jumpered the headlight switch connector).

More Ford 4.9L, 5.0L, 5.8L Tutorials

You can find a complete list of tutorials for 4.9L, 5.0L or 5.8L equipped Fords here: Ford 4.9L, 5.0L, 5.9L Index Of Articles.

Here's a small sample of the tutorials you'll find:

1. Manifold Absolute Pressure MAP Sensor Test (Ford 4.9L, 5.0L, 5.8L).
2. Ignition Coil Test -No Spark No Start Tests (Ford 4.9L, 5.0L, 5.8L).
3. How To Troubleshoot A No Start (Ford 4.9L, 5.0L, 5.8L).
4. Testing A Blown Head Gasket (Ford 4.9L, 5.0L, 5.8L).
5. How To Test Engine Compression (4.9L, 5.0L, 5.8L).
6. How To Test The Ford Mass Air Flow (MAF) Sensor (at: easyautodiagnostics.com).