Mustang won't start all of a sudden, battery good

Sounds like some electrical problem! But the mustang I owned several years ago had the same problems. After putting a new starter an alternator and battery in it the it still would not start. I done some research on it an found out that the key was bad because in had a computer chip in it. I bought a new key for it an it started right up with no problems. Just my advice on the mustang I owned. Also check your fuses.

The battery looks fairly new, I only bought the car last summer so I don't know the battery's exact age. It passed the load test though and has held charge. And with the key thing, I have a spare with a chip which I tried, and got the same result. I checked a few fuses, but not all of them. Should I check all the fuses and relays associated with the ignition circuit? Also, side note, is there any way I can directly connect the battery to the power windows so I can roll them up? Car is stuck outside and it's going to rain soon

Has a BAD ground check all connections MAIN grounds under hood. Needs a voltage drop test preformed on the starter circuit 10 minutes with a multimeter. Then after its running check the Alternator output 13.2 - 14.8 volts

Did you ever figure it out. I have a 06 4.0 doing the exact same thing.

Same happend to mine 2012 Boss. Problem was the imobilizer connected to the alarm. Just satt in the car, activated the larm and deactivated it again a couple of times and she fired up normaly. Hope it helps someone. Greetings from Sweden.

I have a 2011 that I just figured out. It was the starter relay in fuse box under the hood. $11.22 and could have saved myself a battery and starter.

Stepheninski, You Rock! Thank you so much for your post. My son was in Fort Bragg, far from home and his Mustang just wouldn’t start. It was the key. Thank you

Stepheninski you're exactly right just took my relay out cleaned the posts with some alcohol and a wire brush and she fired right up!

No power going to injectors​ on 2005 Ford mustang v6

2013 Boss w same problem. When turning key to start, lots of clicking and flashing, no action. Tripped the alarm key on then off, locked and unlocked doors a couple times. Also pulled the starter relay switch - looked clean & normal, put it back in. Car started right up. Just don't know which trick did it. Will get a spare starter relay switch just in case.

Just had all these issues I have a 2007 Ford Mustang GT had the battery and alternator changed out Star Island too high and I put in the new battery and alternator because the CD player went crazy the car locked up and shut off the new battery and new alternator make the car run good but it still felt like it was trying to cut off and it was Alan out of control the throttle body was cleaned had the oil change and it runs like it's brand new now so all of you who are having problems that keep replacing the battery and the alternator you must clean the throttle body most Ford Mustangs do not have a chip in it to reset it the car is still registering all of the old stuff but once you clean the throttle body it will register just like new

get a new battery and alternator then have the throttle body sprayed out good brushed and cleaned the car will reset itself

the problems are not electrical don't care how much stuff you got hooked up to the battery it doesn't mean it's electrical it means probably that your battery is not strong enough to push your alternator it was something simple as changing the body and the alternator and have the throttle body cleaned

Correction..changing to a brand new battery.. stop buying used batteries

Turn the steering wheel back and forth and mash break pedal at the same time while turning your key worked for my daughter this morning

I have a 2007 Mustang GT with 58,000 miles that I've dealt with this issue twice now due to a dying battery in a key fob. Below is the solution that has worked twice for me. My aftermarket remote fob - not attached to key - with 4 buttons (lock, unlock, trunk, and panic) had a low battery that caused the dash lights/radio to flicker when attempting to unlock the car with the dying remote. Afterwards, the starter wasn't engaging at all. I blew fuse 46 20A in the smart junction box. After replacing fuse, starter would engage but the engine would not crank. Attempted jumping, removing battery and charging to full, using jumper from disconnected neg battery cable terminal to connected POS post in an attempt to clear pcm config, connected scan tool which was showing U1900 (unreadable message from ABS module) and U2011 (ABS Motor). The brake pedal was hard as a rock with maybe a half inch of play. Any attempt to touch the brake with the key in the ON position would throw voltage from 12.6 to 6v and it would jump around between 6v, 9, 7, 10, 8 and after 10 seconds return to 12.6v. I thought I may have blown the Brake Boost Pump Vacuum. After many physical tests with a Digital Multi-Meter that showed nothing unusual, I cleared the Codes with my scan tool, pushed the brake AND HELD IT during the spastic volt shifts and waited until voltage returned to the original 12.6v. STILL HOLDING BRAKE down, after stabilization, I turned the key and the car turned over without an ounce of hesitation. I needed to clear the Codes once more after I reached my destination to rid the pcm of the logged volt fluctuation error when pressing the brake during the first good start since unlocking the doors messed up the computer. After the second clear, the car starts normally and there are no more voltage issues with brake pedal or dash/radio/any other components. I did try all of the above first and none of the above worked for me except what I have written here. Hope that helps someone and yes it does require you have a scan tool with the ability to clear codes to work. I have the OBDLink MX Bluetooth adapter and paid the 10$ for the extra package that allows module specific connection and clearing codes among a few other data point capabilities.

my 1999 Mustang V6 not doing nothing at all , won't start up won't turn over , its not getting fire from the battery the battery is good got it tested . I got the starter tested as well I'm not getting no power from it ... what can be the cause ??

I've got a 96 3.8 that will start once or twice then it wont start at all. Wont turn over, nothing. Then all of a sudden after trying for how long will start and the repeat the process. The battery is good as well as the alternator. The fuel pump is turning on everything works. What could be the problem

I have a 1999 GT. Same issue. Would turn over but not start. I was reading this post and tried the spare key. Started right up. Went back to other key, no start. So how using spare and no problems with starting. Thanks for the input guys!!! Just need a new spare key.

I have a 2002 Ford mustang v6 I had went to pick up my daughter shut the car off when she came out went to start it and it wouldn't start what could the problem be

Thats what ours did today. Ours is a stick shift and we were able to push start the car and it made it home. Before push starting, we attempted to use jumper cables with no luck. We have not found the reason for the issue but alt and battery have been replaced recently. I suspect its a bad ground fuse or relay...will check more in morning.

My mustang is an 2011. After much searching and many helpful ideas and several wasted dollars, the light finally came on in by brain. The no start problem was the main fuse box under the hood. It was the starter relay all the time. This little thing was completely off the radar. In fact Auto Zone at the time didn't even have a replacement part listed in their system. The check it, I removed the fan relay and plugged it into the starter relay spot and it fired right up. I keep a spare in the glove box just in case. God bless.

So l also was having the exact same issues with my 2005 Mustang. I searched and read hundreds.of forums and tried all of the exact same things that everybody has listed in here. Even after putting a brand new battery in it, if l didn't drive it for 3 days, the battery would be dead. And out of the hundreds of answers l read, there was only 1 that was actually right. Some of the things people do and say is the fix may help to remedy the problem for a little while, but they don't fix the actual problem. So this guy said that the problem with the battery draining while the car is off is actually the Shaker stereo which comes in almost all Mustangs for over 15 years now l believe. The only issue l had was with his solution to the problem which was to pop my hood, open the fuse box, and pull the fuse for the stereo everytime l got out of the car. Now that is ridiculous in the 1st place that you should even have to do that with a brand new car, but then Ford absolutely refuses to admit how bad they F'ed up and continued to sell them with these malfunctioning Shaker stereos up to 2014 or 15 l believe. All of the mustangs have the exact same problems up til then. Ford has spent millions of dollars to have every single post just like this removed from every single website or forum that they can find to keep people from knowing how bad they messed up. So they instructed all of their dealerships and mechanics to just replace the battery everytime a mustang was brought in, even while under warranty, and tell the owners that it was a bad battery. Because that was far cheaper than the billions it would cost from actually admitting their true F*@# up and having to recall and actually fix every single one. So l actually setup my voltage meter so that my battery ran through it so l could read how much was being drawn from the battery while the car was off. And it would continuously spike every 10 seconds from .2 volts up to .9 volts and then fall back to .2. Then l started pulling fuses until l hit the one that made it drop down to .019 and that is where it stayed. And that fuse was the Stereo fuse. So l actually wired a shut off switch in my glove box that shuts just that fuse off because there is no way l was going to pop my hood and pull the fuse everytime l got out and back in when getting in to my car. And the stereo still keeps all my presets and settings in memory, it just automatically turns on to am radio everytime l flip the switch back on. Now there is also 1 more problem that l figured out which was causing a whole different slew of problems from my speedometer not working to my blinkers and wipers randomly not working. And that is the passenger side door lets water leak inside of the vehicle, along with the driver door and some holes under the hood also letting water get inside the vehicle, but the passenger side a huge problem because it lets water run right down on the computer and it corrodes and fries the computer boards and pins that plug into it on the circuit boards. If you pull the fuse box apart and actually detach your fuses from by the passenger side floor board, you will see what l mean. This is the real cause of so many of all these other problems that you can't figure out on your Mustangs. So l cut a sheet of poly to fit up in there and taped it to the side wall above the computer all the way across and it drapes all the way down to the floor under the carpet so you can't see it and it keeps any water from doing anymore damage to the computer. I hope this helps save many of you years of trying figure out this ridiculousness. And will certainly save you hundreds of dollars fixing unnecessary things.

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My 2002 V6 has a new battery and alternator, She ran all summer then when I put her to sleep for the winter I started her once a week then all of a sudden she went dead. I'm going to try the starter relay fuse for sure. The battery could have been a bad one not sure. Thank you for all the information on here.