Truck kills when I turn on the headlights???

[Reynolds]

I am having some issues with a 2001 Ford F-150. My truck kills as soon as I turn on the headlights. Also, the truck will not start if the headlights are on. I replaced the front headlamp bulbs to no avail. Secondly, the ABS light is intermittenedly flashing along with the check engine light. I have gone through the fuses, but I have not located any that are out. I also tried unhooking/hooking the positive battery cable, but that also did not help. Has anyone ever heard of this same problem. I am guessing I need to have it brought it and hooked up to a computer.

[Christopher Quast]

Sounds like your battery is shot or your alternator or both and you can check by getting the truck running and watch your amps guage and the needle might flicker and shoot not drop if the alternator is good. Have you ever jump started another vehicle recently? And just for kicks I would bring your battery to your local auto parts store and they can usually test them. Good Luck and let em know what happens

[Scott K]

My first guess would be a weak battery, bad/loose grounds. Other then that possible shorted wires. Weird electrical concerns can be tricky. Will it also die if you turn the heater fan and wipers on? How about just parking lights (first click on switch), disconnect both headlamp bulbs and see if it is the load that kills the truck, or just the fact that the headlamp switch is on. Do you notice anything else? When you said the truck doesnt start with the headlamps on, does the engine turn over, if it does, does it crank slow?

I have seen a quite a few bad gem modules cause weird electrical concerns, this may be a possibility as well. What would happen sometimes is the windshield would leak water and damage the module.

[Jeremy airjer W]

I have seen a quite a few bad gem modules cause weird electrical concerns, this may be a possibility as well. What would happen sometimes is the windshield would leak water and damage the module.

I have had these mysteriously crank the vehicle over with no key in the ignition as well as turn on the windshield wipers whenever!

Sounds to me like there may be a grounding issue?

[Shack]

Quote:

Also, the truck will not start if the headlights are on.

When you say this, do mean it will not crank over or the eng. will crank over, but not fire?

My first question asked when stuff like this is brought up would be "do you have a remote starter or after market alarm?".

Every thing above are good suspects though.

[Reynolds]

The truck will turn over just fine with the lights on, but will not fire. It will start with the parking lights on. It will also run with the wipers and/or heater fan on. When I turn on the headlights with the vehicle not running, the left headlight (new bulb) is much dimmer than the right. Also, with the lights off, and the left headlight removed, the truck will not start.

I do not have an alarm or remote starter and the amp gauge is not flickering. I did however, jump start a vehicle back in January, and not long after, the "Check Engine Light" came on. Since that time I have only driven the truck on five or so occasions because I have been out on the road working. And it wasn't until the other night leaving the Cabela's parking lot that I noticed it would not run with the lights on.

I was doing some research last night on the internet and ended up finding a forum in which another guy described the exact same problems that I am having. Even right down to the left headlight being dim. Apparently a bad ground was a culprit.

I also found a few forums about the ABS light. The problem in those cases stemmed from bad wiring or a rear speed sensor.

Just want to thank you guys for the input and troubleshooting ideas!

[Scott K]

Reynolds keep us informed on what you find, if it is a ground, where is it bad, thanks!

[Reynolds]

I brought it into the shop this afternoon. I will post the details once I hear back on the diagnosis.

[Reynolds]

Turned out to be a bad ground on the left headlight. The ABS light was a wheel speed sensor issue. And, the Check Engine Light had something to do with a differential sensor.

[Jeremy airjer W]

I'll take credit for that one!