Low beam headlights do not work, bulbs and fuses fine

Rowe2ry · 12-19-2010, 02:35 PM

Hey guys, I'm working on a 2004 3.9L V6 convertible. The headlights will not come on. High beams and parking lights work as do the tail lights and brakes. The interior gauge dimmer works but the low beams do not come on. Anything ideas on what is causing the problem?

This ad is not displayed to registered or logged-in members.
Register your free account today and become a member on Mustang Forums!

RyansQuick6 · 12-19-2010, 04:43 PM

There are 2 fuses for the low beam, how did you test the bulbs?

Rowe2ry · 12-19-2010, 04:51 PM

Thank you for replying. The bulbs were just visually inspected (both of them) coupled with th eunlikelyness of the bulbs both burning out at the same time, I ruled them out. Af rot eh fuses, I found the 20 10AMP fuses under the dash for left and right hlow beams and they were both in good shape. As was the "B" fuse under the hood for headlights. Are the switches in these 99-04 cars generally faulty? This car was also recently rear ended with no visual damage. Are there any grounds or wiring locations that could be damaged easily by this?

RyansQuick6 · 12-19-2010, 05:00 PM

The wiring should be fine, but the impact from an accident could have easily weakend the filiaments, and since the lights have been on for the exact same amount of time, the likelyhood of their simultanious demise is very high. I'd recommend upgrading to at least some silverstar bulbs if not HID's. Have you put a voltmeter/test light on the low beam wire at the headlamp connector? If the parking/dash/taillamps are on a different wire than the low beams. I've had my lowbeam wire come loose from the switch connector, it just had to be clicked back into place, but the switch tends to hold up very well.

Rowe2ry · 12-19-2010, 05:08 PM

I will check with the OEM bulbs of the car. these are Silverstars. I will also check the wiring behind the switch. I know the headlights were working for a while after the accident so I am still thinking the bulbs should be fine. Thank you for the suggestions.

RyansQuick6 · 12-19-2010, 05:12 PM

Start by checking the connector at the bulb, that's the best place to look to see if you're getting signal.

Rowe2ry · 12-19-2010, 05:16 PM

I do not have any connectivity testing equipment. I might be able to rig up a 12 volt bulb from a parts bin with some wires, I can get a pretty god idea with that.

Rowe2ry · 12-19-2010, 05:17 PM

Please excuse the crappy typing, the wireless keyboard is running out of batteries and kinda does some weird stuff.

LilRoush · 12-19-2010, 05:58 PM

One thing I've noticed about aftermarket headlights (at least in my cars) is that they can melt the harness that clips into the back of the bulb just enough to have the wires loosen to the point of not connecting. I had a similar thing happen back in the day with some APC bulbs.

Rowe2ry · 12-20-2010, 08:25 AM

Okay, I inspected the bulbs again today and they are CLEARLY blown, I have no idea why they looked fine the first time I checked but I am going to call it user error until I get new bulbs in. the switch was fully connected, the ceonnections all look solid and corrosion free. I'm guessing I just didn't see the break in the filaments last time. Odd that they both went out but the wreck probably weakened them, and a speedbump or voltage spike probably finished them off.