I have a 05 Mustang base V6 auto. Headlights won't stay on. Sometimes high beam works. Everyday it's different. Last night when the fans turned on the lights would come on the off again when the fans turned off. Today I can't get them to stay on more than 2 seconds while the car is running. If the car is off they will stay on as long as you need them to. I've checked fuses and wiring. And replaced the headlight switch. While the car is running, if you turn the headlights on they will stay on for a couple of seconds then go off, turn the headlight switch off then back on they'll come back on for a couple of seconds. Also, occasionally the windows won't work, interior light and the car won't shift out of park (does this all at once) I don't know if the problem is all one thing or not. Any ideas trying to avoid the dealer.

2 Answers 2


Might be a possible alternator failure. You can check the battery voltage. It should be ~12V when not working and ~14ish on idle. This kind of faulty alternator causes something like that.

  • I forgot the solution. At the circumstane you have alternator replacement is the only solution I guess. And then you might need to charge the battery with this new part.
    – coner
    May 11, 2015 at 14:42
  • Radio and everything else works i just cant get the lights to stay on. Everything reads 13 volts. The car has aftermarket halo headlights in them i unplugged the headlights from the harness this morning i had brake lights for 25 mins then all the lights (brake, dash, and interior) shut off. I had to start the car up a couple of times before they would turn back on then 15 mins later i lost all my lights again. May 11, 2015 at 15:38
  • Improper voltage signs faulty alternator in general but not that situation it seems. However I still doubt on alternator. Thanks for the feedback
    – coner
    May 11, 2015 at 19:55

First, remove the illegal, substandard, and defective "aftermarket halo headlights" and the ballasts that came with them, and replace with the OEM lights.

Then repair the damage the ballasts did to the rest of your system when they back-fed your wiring harness with high voltage discharges.

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