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Q: 2007 Mustang Low-Beam headlight on only one side only comes on for 10 seconds then go outs, however high beams work fine!?!?

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I very recently purchased a 2007 Ford Mustang V-6 in great condition, everything for the most part works okay. However just yesterday I noticed that the passenger side low beam light "was out", although the high beams from the same bulb worked fine as do the driver's side low and high beams, I changed the bulb to a new one and nothing, the low beam didn't even come on. So then I changed the part which this "H13" bulb plugs in to, and I rewired it all correctly to this brand new headlight plug. The low beam light then came on for about 10 seconds and then goes off again?!?! Yet the high beam from this same bulb works just fine! What else could it be, after changing both the bulb and its electrical plug which its plugged in to? The original owner prior to me had quite a few after market parts in it, one of which I found dangling in the engine loosely?! It was a "OPT7 Blitz" bullet, does this have anything to do with it?

My car has 80000 miles.
My car has an automatic transmission.

A: Hey there, thanks for writing in about your...

Hey there, thanks for writing in about your 2007 Mustang. The low beam circuit is monitored by the the Smart Junction Box. It’s the fuse box in the right kick panel. Basically what this means is if the resistance, or the current flow in the circuit is not within the specified range, it will turn off the power to it. That’s why you won’t find a fuse for the low beams. It will re-check the circuit every time the ignition key is cycled. The circuit flows from the SJB through the fuse box under the hood, and then to the headlights. Inspect as much of the wiring as you can. Especially where it might have been tampered with for the HID lights. If there is a short to power or ground, or too much or not enough resistance, it will turn off the power. This is not the case with your fog lamps and high beams. They are powered by a relay that is fused, and the circuit is not monitored. It will simply blow a fuse if there’s a problem. If you need more help, consider YourMechanic, as a certified technician from YourMechanic can come to your car’s location to diagnose and repair the headlight problem.

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