jbritt Posted September 13, 2019 Share Posted September 13, 2019 This is post replacing the fried headlight wires, leaving it apart for several months, oh and not taking any pictures before tearing into it.... 86 f250 single cab long bed with dome lights So, I have hi and lo beams, parking brake light, 4x4 light, and nothing else. The following pictures are how the switch is currently wired. the white wire coming from the A pin is the headlight wire that was burnt. I have tried to work my way through three different wiring diagrams and still cant crack this one. It looks as though the power for the brake lights comes through the turn signal/hazard switch ut i have been unable to get power to the circuit. Now the White wire with the blue connector was the other burnt wire that i would which i replaced the bad section of. It is hot at all times and I do not know what it goes to/is for. Below is the connector that is on the other end, it is the black wire with electrical tape that connects to the same terminal as the brown wire. last little thing is the black wire coming from just above the hi beam switch. when I apply voltage the dome lights kick on. just wondering how that ties into the wiring so it is part of the switch circuit. I know theres enough knowledge on this site to answer my questions, I just hope the right people see this! Thank you kindly in advance for any help of tips! Regards, John Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted September 13, 2019 Share Posted September 13, 2019 I would start with the '86 EVTM available in the resources section of this forum. It details the Electrical & Vacuum Troubleshooting of your specific vehicle circuit by circuit, connector by connector, and pin by pin. Each circuit is broken out individually, and all test procedure is detailed. I hate to say RTM!, but please rtm... Link to comment Share on other sites More sharing options...
Gary Lewis Posted September 13, 2019 Share Posted September 13, 2019 Let's take this one step at a time. First, the EVTM Jim referred to is here: Documentation/Electrical/EVTM's/1986 EVTM. And there are several sections you'll need, like Charge & Power Distribution - Diesel Engines; Headlamps; and Stop, Turn, & Hazard Lamps. The reason the truck had problems in the first place is the marginally-adequate-when-new design of the headlights circuit. It had all of the power to the headlights going through a skinny, barely adequate, wire to the switch and then out to the headlights. You might want to read the page here to see how to ensure that doesn't happen again: Documentation/Electrical/Lighting/Headlight Wiring Harness. Now to the problems. Let's start with your first statement: "I have hi and lo beams, parking brake light, 4x4 light, and nothing else." Does that mean nothing else in the truck works? Or nothing else in the lighting? I ask because when diagnosing you have to know what the symptoms are and making assumptions leads to chasing rabbits. As for the white wire, is it a replacement for an original wire? If so, what wire does it connect to? Let's leave it there and pick things up after your response. Link to comment Share on other sites More sharing options...
jbritt Posted September 13, 2019 Author Share Posted September 13, 2019 I would start with the '86 EVTM available in the resources section of this forum. It details the Electrical & Vacuum Troubleshooting of your specific vehicle circuit by circuit, connector by connector, and pin by pin. Each circuit is broken out individually, and all test procedure is detailed. I hate to say RTM!, but please rtm... I will take a look through that today and see where I get with it. I figured there was a rock I hadn't turned over yet documentation wise. and as much as we hate to say it some times, it helps to reminded to rtm from time to time, so thank you for that. Link to comment Share on other sites More sharing options...
jbritt Posted September 13, 2019 Author Share Posted September 13, 2019 Let's take this one step at a time. First, the EVTM Jim referred to is here: Documentation/Electrical/EVTM's/1986 EVTM. And there are several sections you'll need, like Charge & Power Distribution - Diesel Engines; Headlamps; and Stop, Turn, & Hazard Lamps. The reason the truck had problems in the first place is the marginally-adequate-when-new design of the headlights circuit. It had all of the power to the headlights going through a skinny, barely adequate, wire to the switch and then out to the headlights. You might want to read the page here to see how to ensure that doesn't happen again: Documentation/Electrical/Lighting/Headlight Wiring Harness. Now to the problems. Let's start with your first statement: "I have hi and lo beams, parking brake light, 4x4 light, and nothing else." Does that mean nothing else in the truck works? Or nothing else in the lighting? I ask because when diagnosing you have to know what the symptoms are and making assumptions leads to chasing rabbits. As for the white wire, is it a replacement for an original wire? If so, what wire does it connect to? Let's leave it there and pick things up after your response. Awesome, gonna read up on the evtm and how to prevent the meltdown today! As for what i have and dont have, that is in reference to just the lights. To word it better, I have hi and lo beams, all dash lights function except for the gauge illumination/dimmer, and my dome light does not work. otherwise, the truck runs and drives fine (knocks on wood). The white wire is a replacement wire that I put in to replace a section of burnt wire I found. It is the taped black wire indicated with the red arrows: The grey connector is on the drivers side of the vehicle, on the firewall in the engine compartment below the brake master. Link to comment Share on other sites More sharing options...
jbritt Posted September 13, 2019 Author Share Posted September 13, 2019 Awesome, gonna read up on the evtm and how to prevent the meltdown today! As for what i have and dont have, that is in reference to just the lights. To word it better, I have hi and lo beams, all dash lights function except for the gauge illumination/dimmer, and my dome light does not work. otherwise, the truck runs and drives fine (knocks on wood). The white wire is a replacement wire that I put in to replace a section of burnt wire I found. It is the taped black wire indicated with the red arrows: The grey connector is on the drivers side of the vehicle, on the firewall in the engine compartment below the brake master. this was last week (dash has since been put back in) so I wouldn't be surprised if theres a ground missing. Bout to dive in on it with the new info, I will check back in after a bit of digging and let you guys know if i find anything. Link to comment Share on other sites More sharing options...
Gary Lewis Posted September 13, 2019 Share Posted September 13, 2019 this was last week (dash has since been put back in) so I wouldn't be surprised if theres a ground missing. Bout to dive in on it with the new info, I will check back in after a bit of digging and let you guys know if i find anything. That can really be intimidating. So feel free to ask questions. And a black wire is almost always a ground. Link to comment Share on other sites More sharing options...
jbritt Posted September 13, 2019 Author Share Posted September 13, 2019 That can really be intimidating. So feel free to ask questions. And a black wire is almost always a ground. so it looks like I'm missing the two brown wires coming from the R pin on the light switch. this would explain the lack of cab lights, as well as the marker lights. Going to try and trace wires from the marker lights back to the switch in hopes of finding the missing connection. The diagram shows a brown wire going to c906 as well as g909 next to it. I have a brown wire but it has a light blue tracer... are they one in the same? I also am not seeing a ground where g909 is supposed to be. Link to comment Share on other sites More sharing options...
Gary Lewis Posted September 13, 2019 Share Posted September 13, 2019 so it looks like I'm missing the two brown wires coming from the R pin on the light switch. this would explain the lack of cab lights, as well as the marker lights. Going to try and trace wires from the marker lights back to the switch in hopes of finding the missing connection. The diagram shows a brown wire going to c906 as well as g909 next to it. I have a brown wire but it has a light blue tracer... are they one in the same? I also am not seeing a ground where g909 is supposed to be. Ah, you discovered those pages and edited your post. Yes, lack of that wire would explain several things. Tracing isn't easy, but you do have a large part of the cab apart, so maybe you can. Good luck! Link to comment Share on other sites More sharing options...
jbritt Posted September 13, 2019 Author Share Posted September 13, 2019 Ah, you discovered those pages and edited your post. Yes, lack of that wire would explain several things. Tracing isn't easy, but you do have a large part of the cab apart, so maybe you can. Good luck! Im thinking that i just cant see where it is on the diagrams but I cant seem to locate the junction block. Is it the fuse block? Link to comment Share on other sites More sharing options...
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