Low beam headlights not working

Tiny
ALESIA PATTON-MCNEIL
  • MEMBER
  • 2010 LINCOLN TOWN CAR
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 120,000 MILES
Low beam headlight won't work on both sides. How can I test LCM?
Tuesday, April 5th, 2022 AT 11:18 AM

5 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
The fact that both low beams are affected, then the likely cause of this is the LCM, so you are on the right path.

However, we could have a switch issue, so we need to check two things.

First, we need to check the voltage going into the LCM from the switch (technically the voltage is coming from the LCM and the switch is grounding it).

Here are a couple of guides that will help with this:

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Then we need to check power from the LCM to the head lights on the low beam.

I suspect you will have voltage on the switch circuit and not out of the LCM on the low beams which means the LCM is the issue.
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Tuesday, April 5th, 2022 AT 7:22 PM
Tiny
ALESIA PATTON-MCNEIL
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Okay, what if both of those have power?
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Wednesday, April 6th, 2022 AT 3:27 PM
Tiny
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Take a look at the first wiring diagram.

When you say both have power, I assume you mean power in and out of the LCM. However, you have both circuits for the head lights with power?

If you do then the bulbs, wiring, or grounds are the issue. However, this is rare to be an issue on both circuits. It is far more likely to be an LCM issue but if you have 12 volts on those circuits then the LCM is fine.
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Wednesday, April 6th, 2022 AT 3:39 PM
Tiny
ALESIA PATTON-MCNEIL
  • MEMBER
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Well, after further checking the light switch on dash has power on sentinel and off position, but no power in the on position.
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Wednesday, April 6th, 2022 AT 5:10 PM
Tiny
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Okay, great. So, we need to replace the switch? I am attaching the info below from the manual on how to do this if you need it, but these Ford products made it really easy.

Let me know if you have other questions. Thanks
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Wednesday, April 6th, 2022 AT 5:30 PM

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