runaway parents Posted February 21 Report Share Posted February 21 So last fall before I shut the truck down for the Winter I installed new headlights .They seemed to work fine So just recently I got in the truck fired it up. Got a message on the dashboard that's stated headlight low beam open circuit left side. And then the marker light quit working also . anybody have a wiring diagram 4 the headlights on A 08 VNL 780? Any ideas why It just quit working? It makes me wonder If it hasn't been attacked by some wire chewing critters . Oh is this going to be fun.I have noticed squirrels milling around the truck. Also seen raccoons out there.If they are found guilty of chewing on my wires oh man it's on . I may have to ask for recipes that involve squirrel and racoon. Quote Link to comment Share on other sites More sharing options...
rickeieio Posted February 21 Report Share Posted February 21 (edited) Since you have a Volvo, I'd say take a look at the top of the frame rail next to the driver side of the radiator. Right where you likely stepped to reach something. Peal the harness cover back and take a peek. Just remember, it's nearly always the ground.😁 Edited February 21 by rickeieio Quote Link to comment Share on other sites More sharing options...
Parrformance Posted February 21 Report Share Posted February 21 8 hours ago, rickeieio said: Since you have a Volvo, I'd say take a look at the top of the frame rail next to the driver side of the radiator. Right where you likely stepped to reach something. Peal the harness cover back and take a peek. Just remember, it's nearly always the ground.😁 Might also want to look at the connection for the a/c compressor, by that step🙁 Clean and mark with bright tape to avoid stepping on them till they get disconnected. Quote Link to comment Share on other sites More sharing options...
runaway parents Posted February 21 Author Report Share Posted February 21 Is just put a Test light on everywire coming out of the headlights and for some reason every wireComing out of the headlights Is hot And no lights are on. I am thinking bad head light fixture Quote Link to comment Share on other sites More sharing options...
ddm502001 Posted February 21 Report Share Posted February 21 Sounding more like lost ground Quote Link to comment Share on other sites More sharing options...
runaway parents Posted February 22 Author Report Share Posted February 22 (edited) 3 hours ago, ddm502001 said: Sounding more like lost ground What color wires Is typically ground. And how can I test the headlight to find which wire is ground. Edited February 22 by runaway parents Quote Link to comment Share on other sites More sharing options...
Parrformance Posted February 22 Report Share Posted February 22 https://www.hhrvresource.com/node/179.html When I get a chance I will sit down and double check, but I want to say whit wire for ground. Great chance to play swaptronics, if the passenger side headlight is working, unplug the driver side, remove the three or four bolts, then carry it over and plug it in to the opposite side. Thus should help you isolate what is isn’t working. Quote Link to comment Share on other sites More sharing options...
Deezl Smoke Posted February 22 Report Share Posted February 22 10 hours ago, runaway parents said: What color wires Is typically ground. And how can I test the headlight to find which wire is ground. "Typically", not absolutely, but typically in a mobile 12 volt dc system, black is ground. LED lights need a different testing procedure than incandescent. Incandescent will have continuity both directions so it does not matter which way you hook the test leads. LED is a one way diode, so the test leads will have to be oriented in the correct direction. It will take someone with way more knowledge and experience than I to confirm or deny what I'm about to say, but.... So the fact that your dash tells you there is an issue with a headlight, the light circuit goes through the ECM. "I've heard..."🙄 that improper draw, and/or any corrosion even at the ecm pins, can trigger a code like you are experiencing. So even though you have power at the light plug, does not mean you have the correct voltage or correct amperage when hooked up, to satisfy the ecm. IMO. Someone please confirm or deny this. I would, in the mean time, go to the ecm and carefully check for corrosion at the multi-pin connections, or a sunken pin etc. Quote Link to comment Share on other sites More sharing options...
ddm502001 Posted February 22 Report Share Posted February 22 Agree with the above, some trucks it reuires a Wiring Diagram as some do not color code to a set standard but their own. Three wires on a Hi/Lo beam one has to have continuity to ground Unplugged, the other two power off dimmer system while unplugged. Quote Link to comment Share on other sites More sharing options...
rickeieio Posted February 23 Report Share Posted February 23 There are a couple grounding lugs on the firewall with lots of wires going to them. I bet they're all the same color as one of those headlight wires..... Quote Link to comment Share on other sites More sharing options...
runaway parents Posted February 23 Author Report Share Posted February 23 OK well thanks for The info. I think I've got My issue with the headlight fixed. Yes it was a bad ground Didn't find any evidence of critter's chewing on wires. So the squirrels and raccoons are safe for now. Thanks again for the help. Quote Link to comment Share on other sites More sharing options...
GlennWest Posted February 24 Report Share Posted February 24 Yes a test light can fool you. You are making the ground with it.. Quote Link to comment Share on other sites More sharing options...
Lou Schneider Posted February 24 Report Share Posted February 24 (edited) "Every wire is hot" is a sign of a missing ground. Without a ground all points in the circuit are pulled up to the supply voltage. The test light doesn't draw enough current to replace the ground so it lights up when it sees voltage on the should-be-grounded side of the bulb. Edited February 24 by Lou Schneider Quote Link to comment Share on other sites More sharing options...
.thumb.jpg.8e7515f6531fe4ed872eaa7b0f6c22c1.jpg)
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.