Hello All,
I have a 1995 F250 7.5l 4wd SuperCab. When I pull the headlights on the engine cuts off. It will run with the marker lights but not the headlights. I have replaced the headlight switch and still have the same problem. Have checked my battery and alternator both under load and not under load and they are fine. I have checked all the grounds I could find, cleaned them and tightened them all up. I also replaced my positive and negative battery cables after this problem started and still have the problem. Any help would be appreciated as I’m about to send the truck to the Ford dealer to have them troubleshoot but that will cost a fortune. I appreciate your time and your expertise and your help,
Grant

 

Does it cut out when you just flash the headlights or hold the multifunction switches stalk back?

 

The engine does not die when I flash the lights or the other functions. It only dies when I pull the headlights on. Truck runs fine with the market lights. Replaced the headlight switch thinking it was that but sadly no!

 

Sounds like it might be a bad Idle air control valve that does not change when the load on the engine increases.

You should run the KOEO electrical self-test and if it passes then run the KOER actuator self-test to check the Idle air control valve operation.

 

have to retract my last response. The engine does indeed die when you flash the brights. I’m at a loss!

 

Your headlamp circuit is interrupting your engine ignition or fuel systems which I would start diagnosis at the harness for the lights and follow it around to make sure it’s not damaged or weird looking

 

Still think as I did in post #4 above.

 

I feel like a load to be that intense would require more than 2 headlamps flash to pass unless this battery is boinked and the alternator charges in IOUs
like i could see the bad battery scenario and a load like that if it’s causing the ignition to interior or be too weak. Or if there is a bad short to ground and that does it too. But I think that still means inspecting his harness is a good idea at headlights and it’s never a bad idea to at least clean the IAC even if not replace. Can verify function while at it

 

Ran key off and on tests yesterday the only code I got was from the EGR Valve. The electrical system passed the tests. I will start inspecting the headlight wiring harness starting with removing the bulbs and seeing what happens. Did a load test on the battery and it was fine and the alternator also is charging fine. Still chasing down ground checks as well.

 

was the system under load when checked the alternator?

 

I checked it with the engine running and engine off.

 

that’s nice but did you load test the charging system.

a carbon pile of a dedicated battery tester with a. Charging system checker is best for this. Autozone does it

 

I have to agree with post #4. This is not a wiring problem. If it were a short in a high amp draw circut like the headlights it would have blow fuses, fuseable links, or burt wires by now. My guess is either engine idle is to low and not bumping up under the load or bad alternator trying to seize ubder the load. What happens if you incresae the RPM to1500 before you turn on the headlights? Does the alternator make any noise when under a load, like with the AC (if equiped) the blower on high and the running lights on.

 

Well it’s fixed! I removed the headlight wiring harnesses and cleaned them, added some dialectical grease and hey presto problem fixed! Now I did some moving around all the harnesses in the engine compartment checking for problems so I don’t know if I solved a grounding problem or a shorting problem. Alternator and battery were both checked at autozone and are in top shape! I knew they would be, the battery is less than three months old and a brand new alternator about six months ago. Thank you all for your help now on to trying to get a 26 year old EGR Valve Pipe off without breaking everything off!

 

interesting.. did any connectors or parts have anything to note? Like i had rusty mud inside a fuel injector connector before, quite noticeable when i checked it. but like, you see anything? Terminals bent? Corroded? Wires with rubbed insulation? Does the headlight harness only connect to the headlights or does it have other components that follow it?

im kinda surprised it worked.. which makes me think a short to power or a ground path something that shouldnt be using it takes when you hit it.