Just bought this truck a few months ago, that being said about a week ago the problems started. I have a 2006 Ford F150 STX with around 179.000 miles on it. A few weeks ago my battery light started to come on, but the gauge did not drop, so I monitored it and kept driving it. This lasted about a week before i noticed that the gauge started to drop while running, so I knew i would be buying an alternator soon. Sure enough two days ago it died and i swapped out the alternator and was back up and running with no troubles, until today that is. I went to the store, and when i came out my truck would not start, no crank no start. I popped the hood to take a peek at things to make sure i did not forget to button up the alternator installation. Everything looked fine so i got back in turned the key and it fired right up and back home I went. When i shut it off i tried to start it again and same thing no crank no start. It was late so i let it sit over night. Next morning i came out and tried to start it and it went on the first try. Shut it back off and tried to restart and nothing. Since the last time it started i can not get it to restart again. This is the troubleshooting i have done so far. I checked the battery connections and made sure everything was good. Then i opened the fuse panel box on the passenger side and started to check fuses and relays. I watched a video on Youtube where the PCM relay gets corrosion on it so i checked mine pulled it put it back in and it started right up. So I figured this was my fix. Shut it off and tried a restart and again nothing. So i swapped out the relay with another and still will not start. I would like to note that i can hear my fuel pump turn on when i turn my key on. Basically i am not sure what else i can check. Sorry this is so long just wanted to give as much information as possible. Any help on this would be greatly appreciated as i just made my second payment on this truck and i can't even enjoy it.

 

There are several specific observations that need to be made to determine if the problem is power/ground or a control issue:

DO THESE IN ORDER

1. Turn the key from OFF to RUN (not START). What does the THEFT light do? If it stays on for 1-2 seconds and goes out (normal), go to step 2. If it fast-flashes, PATS is activated and engine starting is inhibited. Troubleshoot PATS system.

2. Turn the head lights on. Observe them when the key is turned to START. During a NO CRANK instance, do they stay on, perhaps dimming slightly (normal, go to step 3) or do they go off or or nearly so? If they go off, you have a problem with the battery (load test it - google it) or the primary battery cables or connections, regardless of how "good" you think they look (perform voltage drop tests - google it).

3. Check the control signal for the starter. Does it go HOT when the key is turned to START or not? If not, troubleshoot START signal circuit from ignition switch. If the signal is good, the starter is most likely failing but additional tests are needed to verify.

 

Thank you for the reply. The theft light is acting as it should Normal. Also when headlights are on and I crank the key they stay nice and bright, which is also Normal. As for checking the control signal for the starter i am unable to do this as the truck is not in a garage and it has been raining here non stop for a week. I am hoping that i can get to it soon, I will post any finding. Thanks again and hopefully i get this sorted out soon.

 

At least you've eliminated the first two possibilities.

Need to know if you have an auto or manual transmission.