To dim all headlights

Tiny
LEECARLETON2316
  • MEMBER
  • 1994 MERCURY TOPAZ
  • 2.6L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 125,000 MILES
When I start my vehicle and I have my headlights on they are at one brightness and then as I drive my vehicle it's to me it seems like the headlights go dimmer and stay dim and sometimes it doesn't even do that it just when we started or even our driving it after a while and have to turn the headlights on automatically. I've replaced the bulbs I've replaced the headlight lens. The high beams are the same brightness as the low beams until you hold in the high beam blinker switch module in between high and low beams then it is actually brighter than the normal high beam s are how do I fix this and what could be the problem.
Saturday, March 13th, 2021 AT 9:26 AM

1 Reply

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Just to be clear, you are saying the headlights look correct when you turn them on with the engine off but then when you start the engine they are dim?

Here is a guide that will help with this:

https://www.2carpros.com/articles/one-headlight-is-dim-or-dull

However if they look ok with the engine off then I suspect the issue is a voltage supply issue when all the other systems are on. Basically when the engine is off, you are running off just the battery but there is nothing really on except the headlights, maybe the radio. Then when you start the engine the alternator is what is supposed to supply the proper voltage to run all the systems including the headlights. The fact that the headlights are not as bright shows that other items are stealing some of the current needed to keep them bright.

Does this make sense? I would test the alternator and make sure it passes. Here is a guide to do this:

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Let me know if you have questions. Thanks
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Sunday, March 14th, 2021 AT 7:04 PM

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