Ford F150 - Turning on Headlights Shuts Truck Off

I hope somebody can help me. This evening when getting into my truck it would not start. I always have the headlight switch set to the automatic on position. When I tried to start the truck it wouldn't start up. I made sure the gear selector was in park and started fumbling around with the headlight switch in case I had a dead battery and noticed it would start fine when the headlights were in the off position . After the truck started I turned the lights on in regular mode and it shut down the engine!!! I then tried every putting the switch in every imaginable position and the truck would only start or run when the switch was off.

Out of frustration I started to drive the truck on a well lit road for a few hundred feet until I had to turn onto an unlit street. While driving I turned on the headlights and this time it didn't shut the engine off. I didn't dare mess with the switch again until I got home. When I did get home everything works properly now!!! I'm happy that the truck is running right now, but am afraid this will happen again leaving me stranded.

If anyone has a clue as to what might be happening (or know somebody who has had this happen) I would be thankful.

That sounds really wierd. Must be a short in the wiring or something of that nature to kill the motor. I am really suprised it just doesn't blow out you bulbs.

But I am no electrical genuis.. but I would think it would be a short somewhere.

I was looking at the schematics of the 2005 headlamp and autolamps circuits and a few theories came to mind, but also a few questions. When you said it wouldn't start, did you mean crank no start, or no-crank, no-start? Also, when it died on you when you turned on the lights---did it die right away? Did any other lights come on? Also, did the headlamps work.
If it was a crank, no start---was the theft light blinking real fast and also was the instrument cluster lit up?

Basically one of those weird electrical concerns.

Oh, do you have any other add-ons and do you have the normal trailer plug on the back?

Hi CollinsTech,

Thanks for the quick reply .

It was a no crank, no start situation. Total silence.

The interior lamps would come on and so did the cargo light. The headlights would also come on, but the engine wouldn't crank at all. As a matter of fact, I used my remote keyless entry to unlock the vehicle and the lights all lit up normally when I pressed the unlock button on the key fob.

To be honest, I didn't pay attention to the anti-theft light. Also, I have never made any modifications whatsoever to the truck. It is as it came out of the showroom and only has 6K miles on it. It does have the trailer plug that came with the "tow & go" package but I have never used it. The only odd thing I have been noticing is that the gas gauge is very erratic. I filled the truck up about two hours before the light problem and despite the low fuel light being on, it could only take 16 gallons with a 27 gallon tank.

I'm hoping the light issue was related to the anti-theft device and that this is an isolated incident. I don't understand the technical specs of this device. I imagine it disables the vehicle in some manner, but I've never given it a thought .

Thanks again for your response! I will sleep a little better tonight knowing it may be some isolated quirk.

I look forward to any "theories" you may have until I can get it into the dealer for some diagnostics.

John

OMG, When I finished wring my last post I started thinking about my filling up the gas tank and said to myself "Shoot, did I forget to put the gas cap back on?" Sure as heck I just went outside and the gas cap door was open and the cap was off.

Could that have caused my problem or was it just a coincidence?

I feel really foolish right now lol.

LOL!!!! No, it's not the gas cap. That shouldn't have anything to do with it.
One thoery I have is related to the instrument cluster. Since the cluster is actually a programmable module that also controls the anti-theft (PATS) system. Plus the headlight switch and its' circuits go through the cluster, it may be related. I will think about it some more and look at the schematics when I get the chance and see if anything else jumps out at me. Let me know if anytihng else weird happens or you can think of anyting else.

Well, the light problem acted up again this morning on my way to work. When I got to work I called my dealership and have an appointment scheduled for Thursday morning.

Amazingly the truck was fine this evening . I'm completely baffled as is the service rep at the dealership. He said he never heard of such a thing occuring in his 20 years as a Ford tech.

I will post whatever they dianose on Thursday.

Thanks again.

John

I thought about it some more and I may have to lean towards a water leak getting into either the junction box(fuse box) or into some other electrical device. Water can cause some crazy electrical problems. One other concern, may be a ground issue. You may have a gournd some where that is loose.
Have to agree with the advisor you talked to. Never heard of headlights being on, causing a no-start condition and I have been in the business a little over 16 years.
Good luck--keep us posted.

You hit the proverbial nail on the head CollinsTech! It is the instrument cluster that they believe to be faulty. The Service Manager picked up on the problem when he had to move my vehicle to the location where they park the vehicles awaiting service. He noticed the gas gauge was erratic and told me he is ordering a new instrument cluster and that I will have to bring him the second PATS key so he could program the new cluster.

What really ticked me off is when I dropped the vehicle off this morning the vehicle was not acting up and he told me "if there's no problem now, I have no way of finding out if there is a problem." He then said "I will keep the vehicle for two days and if the truck doesn't act up I can take it elsewhere because I need the loaner car back." I got really angry and asked him how in the heck can he arrive at a conclusion without even looking at the vehicle. He said "well it doesn't make sense because I've never seen or heard of any problem with headlights shutting off a truck." I was shocked, amazed, and downright insulted by his arrogance. I laid into him (plenty of four letter words) and told him there is always a first time for everything. That sarcastic jerk responded by saying "it's just a truck, not the space shuttle...not too complex." I just walked out and went back to my office. After giving it some thought I became more angry and drove back to the dealership and threw the keys to the loaner along with the loaner vehicle papers on the counter and told him I wanted my truck back NOW!

His tune had changed and that's when he told me about the problem he noticed with the instrument cluster. I gave him a bit of a tongue lashing and he seemed embarrassed so I decided to give him a chance to fix the vehicle and went back to work.

If I had the time and knew of another Ford dealership that wasn't 30 miles away, I would have still taken my truck back. But he seemed somewhat apologetic, I decided to let him have a shot at it. I will probably regret it, but I've known this guy for years and figured he was just having a bad day. He has always been helpful and pleasant in the past and we live in the same small town. I just hope I made the correct decision .

I truly believe what helped him arrive at his diagnosis was the fact that I had printed out your posts and he must have read them after I left.

Thanks again for the great advice!

John

Glad that wasn't my service advisor you talked too-----LOL!!!! Hopefully you are right and it was a bad day for him. Let me know if they get it fixed. Hopefully the cluster fixes it. Good Luck.
Sometimes the advisors come across the wrong way---sometimes their people skills need a little more work.
OOOPs, excuse me. You said Service Manager---they are worse, they think they know everything. Hopefully he is right.