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Ford F-150/F-250: Why Does My Interior Dome Light Stay On?

What do you do when you your dome light stops working on your Ford F-150 or Super Duty?

By Thom Cannell - September 18, 2014
Contributors: double ott ex

This article applies to the Ford F-150 (2004-2014) and the F-250, F-350 Super Duty (2005-2014).

The interior light in your Ford F-150 or Super Duty truck is very important. We usually take it for granted, but we don't know how important it is until we lose it. Without it, you can't find a dropped cell phone, a tissue, or even notice the look of love on your date's face. If your dome light is out, follow these steps and find the light.

Material

  • Voltmeter with alligator clip
  • 12V electrical tester
  • Scan tool

Step 1 - Check light bulb and fuse

Check to see if your light bulb is burnt. Remove your bulb, and check for any change of color. You can also shake it very softly, and if you hear rattling, it means it's indeed burnt. If it is, replace it. Also check your interior dome light's fuse. If the strip is broken, the fuse is blown, and needs to be replaced.

Figure 1. Check your dome light bulb.
Figure 2. Check to see if strip is broken.

Step 2 - Use a voltmeter

Take off the lamp and connect your voltmeter to the lamp module as shown in the image below. Attach the red probe to the positive connector and the black probe to the negative connector.

Choose a range in your voltmeter between 10 and 14. Watch the voltmeter's needle to determine if you're getting any voltage out of your 12 volt dome light. If there is no issue with the voltage, the needle should be steady at around 12 Volts.

Figure 3. Use a voltmeter.

Step 3 - Do the lights ever work?

If your lights work occasionally, you have a loose connection and will have to follow each circuit to the GEM (generic electric module) that controls it. If the lights work for 1-2 doors, check the button switches in the door jamb. Remove the button switch, check for continuity, ground faults, and switch function.

Figure 4. Check the switch.

Step 4 - Check for corrosion

Figure 5. Check for corrosion.

Check the wires connecting to your dome light lamp by removing the light bulb, pulling the connector out, and checking for any corrosion. The older and more Northern your truck the more likely corrosion has interfered with every electrical connection, regardless ever being touched. Our choice fix is a spray with DeoxiIT from Caig Labs. It works and is worth its price.

Step 5 - Use the scan tool

Figure 6. Use the scan tool.

Your scan tool may identify dead modules or relays. Some relays can be interchanged to test. Many modules and relays can be tested for power-in-out with a voltmeter. Check the battery saver relay, the interior lamp relay, the GEM. The scan tool will give you the codes related to the issue. Craftsman, Actron, and Autel are very popular brands.

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