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

TEST 1: Jumpering The Headlight Circuit

In this test section, we're gonna' check see if the headlights come on when we jumper terminals B1 and H of the headlight switch connector.

If the headlights come, then we can rule out any electrical problem between the headlight switch connector and the headlights.

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 B1 and H. Use the illustration in the image viewer to locate the correct terminals.

2. 2

   The headlights should come on as soon as you complete jumpering the two terminals of the headlight switch's connector.
   
   NOTE: If the headlights don't turn on, turn the key to the On position. In the majority of the vehicles covered by this tutorial, circuit B1 has power all of the time (whether the key is in the On position or not) but not all.

Let's take a look at what your test result means:

CASE 1: The headlights 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 B1 is getting power (12 Volts).
2. That circuit H and everything in between the headlight switch connector and the headlight connectors (like the dimmer switch) are feeding power (12 Volts) to the headlights.

The next step is to test the continuity between pins B1 and H of the headlight switch itself. Go to: TEST 2: Testing The Continuity Of The Headlight Circuit.

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

If, after double-checking your connections and retesting, the headlights 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 B1 has power (12 Volts).
2. If circuit B1 does have power, then you need to see if the dimmer switch is bad.

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 2: Testing The Continuity Of The Headlight Circuit

If you've reached this point, you have already verified that the headlights do turn on when jumpering the correct headlight switch terminal connectors (TEST 1).

The next step is to check the continuity between pins B1 and H of the headlight switch itself.

If there's no continuity between this pins, when you test them with headlight switch in it's ‘headlights 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 ‘headlights on’ position.

2. 2

   Test for continuity between pins B1 and H.
   
   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 ‘headlight'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 take a look at what your test results mean:

CASE 1: The multimeter registered continuity when you pulled the headlight switch knob to the ‘headlights on’ position. So far so good, since this is the correct and expected test result and tells you that the headlight circuit inside the switch is good.

CASE 2: The multimeter DID NOT register continuity when you pulled the headlight switch knob to the ‘headlights 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 B1 and H, you can confidently assume that the headlight switch is bad and needs to be replaced (even more so if in TEST 1 the headlights came on when you jumpered the headlight switch connector).