Headlights Kills the Engine
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5th Wheeling
Joined: Oct 2017
Posts: 42
Likes: 6
Headlights Kills the Engine
This seems strange. 1994 F250, 460, 2WD, automatic. My son's truck. This truck has given us a lot of problems with starting/not starting and charging/not charging. I thought we had them all addressed, but today I had to rescue him again. The entire truck had no electrical power, and the issue was a loose (ie broken) battery ground cable. But after correcting the ground, now then engine starts fine, but when you turn on the headlights it kills the engine. Every time. The running lights and taillights do not kill the engine. Any ideas?
Laughing Gas
Joined: Jan 2023
Posts: 1,172
Likes: 114
I doubt it has anything to do with it, but I have some aftermarket KC lights on my truck. The distributor cap was old and the cap caused a no spark condition when the KC lights relay was plugged in. So I replaced the cap and while I was there the rotor and it was fine, it had spark again.
Logistics Pro
Joined: Nov 2013
Posts: 3,922
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From: Mojave, Ca
When a vehicles has a bad large-ground, the starting current tries to find another way to ground and it's through smaller ground wires. Sometimes, it results in the harness burning up and requiring major harness tear down and repair.
But the easiest thing to do is check your existing ground connections and inspect them for tightness and burning. The ones you'll be most interested in are the ground wires near the headlights.
Ground terminal 100 (G100) is common to both your left headlight and your ECU relay. It's located on the backside of your radiator support near the left headlight.
Ground terminal 101 (G101) is common for both your right headlight and one of your ECU sensor grounds. It's located inner right fender, next to your battery.
But the easiest thing to do is check your existing ground connections and inspect them for tightness and burning. The ones you'll be most interested in are the ground wires near the headlights.
Ground terminal 100 (G100) is common to both your left headlight and your ECU relay. It's located on the backside of your radiator support near the left headlight.
Ground terminal 101 (G101) is common for both your right headlight and one of your ECU sensor grounds. It's located inner right fender, next to your battery.
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5th Wheeling
Joined: Oct 2017
Posts: 42
Likes: 6
That was it. The grounding system. Why Ford decided to make ground so complicated I don't know, but establishing a really good battery ground to the body, cleaning up and re-establishing both headlight grounds solved the problem, and the headlights are brighter, too. Thanks!
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