Need help diagnosing an issue
Thread Starter
|
New User
Joined: May 2019
Posts: 2
Likes: 0
Need help diagnosing an issue
I have a 82 f100 with 300i6 that wont run if you turn on the headlights. I can run a straight wire from the battery to the coil and it will run with lights on. Iv tested voltage at idle and it puts out 14v. And ground wires look to be all good so im lost what it could be
Moderator
Joined: Jan 2001
Posts: 56,977
Likes: 2,734
From: Virginia
Do you have a set of jumper cables? If you do, take the negative side and hook one end to the battery negative, and clamp the other end to something that is bare metal on the radiator support. There may be a bolt or something that is not too rusty that you could try. See if that makes the problem go away.
Lead Driver
Joined: Nov 2013
Posts: 7,162
Likes: 1,169
Quite the unusual scenario.
This 14v you measured: Was that right on the battery posts? For the most useful results, measure right on the posts, not the cable ends.
Was that measured with the lights on or off? Actually, I'd like to see both with the engine running, in case the voltage drops too much when you turn on the lights.
Does the engine die immediately when you turn on the lights? Any sputtering, or just bam and off?
This 14v you measured: Was that right on the battery posts? For the most useful results, measure right on the posts, not the cable ends.
Was that measured with the lights on or off? Actually, I'd like to see both with the engine running, in case the voltage drops too much when you turn on the lights.
Does the engine die immediately when you turn on the lights? Any sputtering, or just bam and off?
Cargo Master
Joined: Jun 2013
Posts: 3,177
Likes: 15
From: Somewhere n North America
You can't look at a ground wire or ground connection and determine if it is good.
You would have to measure the resistance or clean the connections.
You would have to measure the resistance or clean the connections.
FTE Legend
Joined: Nov 2015
Posts: 30,876
Likes: 4,116
From: Angier, NC
You had something else going on and moved it the same time you replaced the dimmer.
You are right " As these trucks age, things get corroded and rusted".
Dave ----
Laughing Gas
Joined: Feb 2016
Posts: 817
Likes: 27
I don’t like to throw parts at problems either but these trucks have a long history with melting headlight switches, so replacement is not without merit even if it doesn’t fix the issue. Upgrading to the headlight relay setup is also a plus.
As an example of how much goes thru the headlight switch, my horn wouldn’t work unless my headlights were on. Took awhile to figure that out. New switch fixed the issue.
As an example of how much goes thru the headlight switch, my horn wouldn’t work unless my headlights were on. Took awhile to figure that out. New switch fixed the issue.
Trending Topics
Thread Starter
|
New User
Joined: May 2019
Posts: 2
Likes: 0
Quite the unusual scenario.
This 14v you measured: Was that right on the battery posts? For the most useful results, measure right on the posts, not the cable ends.
Was that measured with the lights on or off? Actually, I'd like to see both with the engine running, in case the voltage drops too much when you turn on the lights.
Does the engine die immediately when you turn on the lights? Any sputtering, or just bam and off?
This 14v you measured: Was that right on the battery posts? For the most useful results, measure right on the posts, not the cable ends.
Was that measured with the lights on or off? Actually, I'd like to see both with the engine running, in case the voltage drops too much when you turn on the lights.
Does the engine die immediately when you turn on the lights? Any sputtering, or just bam and off?
Sometimes it will rum a few seconds sputter and die and sometimes it just bam dies. And it sputters with signal lights but wont die
Last edited by ctubutis; Jun 1, 2019 at 08:25 PM. Reason: fix quote
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Moderator
Joined: Jan 2001
Posts: 56,977
Likes: 2,734
From: Virginia
If the headlights and other lighting up front does not have a good ground, when you turn the lights on the electric will "search" for any place to find a return path to ground. Sometimes this will end up being other circuits in the truck. It may be the ignition circuit in your case, which kills the spark to the engine when the headlights are turned on.
Thread
Thread Starter
Forum
Replies
Last Post
meck1
1987 - 1996 F150 & Larger F-Series Trucks
4
Mar 3, 2015 05:12 PM
1978fordf250
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
4
Feb 3, 2008 06:11 AM
restoringmy46
1948 - 1956 F1, F100 & Larger F-Series Trucks
16
Sep 28, 2007 01:11 AM