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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

engine shuts off when you turn headlights on

 
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Old 01-19-2010, 01:36 PM
whiting5
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engine shuts off when you turn headlights on

last night hopped into my truck 95 f-250 pulled on headlights engine dies? wtf will run with marker lights on but dies when you pull light switch....load tested alt. and battery they check out fine. replaced switch today with new one does the same thing. only other thing that has changed is alt. bearing was making noise now quiet as can be.and this problem starts.... any ideas out there....
 
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Old 01-19-2010, 02:41 PM
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your alt might be fine... but its not Creating enough Juice it sounds like,,, check the cables make sure there ok .. if worst comes to worst get a 200 amp alt you can pick on up for 79 bucks online ....
 
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Old 01-19-2010, 04:21 PM
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My money is on the alternator. They do weird things when they go (or are about to go) toes up.
Roger
 
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Old 01-21-2010, 12:59 PM
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Did you figure this poblem out? I had the same symptom from a bad ground. Replaced the negative battery cable & grounded it properly the problem was cured.
 
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Old 01-21-2010, 01:50 PM
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ugh!!!

so let set couple of days.this morning went and puleed plugs off headlights to see if it would still act up...wouldnt start.just cranks.put headlight plugs back on bulbs truck starts turn on headlights works fine.dont know what to do know...?????
 
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Old 01-21-2010, 02:44 PM
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Something in the ignition or fuel pump relay circuit is grounding through the headlights.

With the headlights unplugged, do you hear the fuel pumps run when the key is turned to ON?
If no, fuel pump relay circuit problem. If yes, ignition circuit.


I have a grounding schematic from Ford for an '89. It should be similar. Tell us the results and I'll find the right chart.

good luck,
 

Last edited by lmd91343; 01-21-2010 at 02:44 PM. Reason: spelling
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Old 01-21-2010, 09:37 PM
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when the headlights were unplugged.the fuel pump kept running.cranked but would not start.
 
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Old 01-21-2010, 09:46 PM
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I'll look over my schematics tonight. Mine are for a 1989. It should be very close.
 
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Old 01-21-2010, 09:47 PM
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A 351, 460 or diesel?
 
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Old 01-21-2010, 10:21 PM
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Whiting,
What is your name?

The ecc power relay and the pcm (computer) grounds connect at a splice to a wire in the loom near the brake sensor leads. That wire runs from there to a ground point behind driver's side headlight where it connects to the left side headlight ground. There it is grounded to the frame or body between the headlight and the inner fender.

As I recall, it is on the radiator support on the back side. I cannot check now, there is a horrible thunderstorm now. I don't keep my truck in the house.

There is another wire at that left headlight ground point that runs to a mirror image ground point behind the passenger headlight. That right hand headlight ground point connects directly to the battery.

All of these wires are black. They are circuit number 57, if you see any paper tags on the loom.

First use your dmm to check continuity of that wire and make sure all the ground connections are clean and greased. Then check the voltage from the positive battery terminal to those ground points.

Of course, failing that trouble shooting you could run a ground wire from the three computer grounds and the power relay to a good ground. But you would still have future ground problems to the other things hooked in the those ground points.

The computer is very sensitive to the voltage. A voltage drop of less than a tenth of a volt could cause engine issues. I could go on and on about that.

Good luck,
 

Last edited by lmd91343; 01-21-2010 at 10:23 PM. Reason: spelling on words connects and these
 
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