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rig light problems

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  • rig light problems

    I have read a number of ford and superduty forums with no luck so i thought i would post here to see if some one else had the same problem. Lost front and rear marker and tail lights on my 02 superduty service truck. i have dash lights and sunvisor lights ( power to sun visor is spliced in at light switch )Checked all fuses and relays , tried new light switch, pulled some of the dash apart and wire is in good shape and has power. Pulled all cab connectors on firewall/ fender and all connector pins are good. No corrosion or melting. I had under hood wire harness completely apart before to find a bad spot in my power wire to alternator and im really not looking forward to doing it again. It has to be before the wire splits to the front and rear of the truck. I first thought it was from hosing the floor out ( work on strip job so mud is a big problem , gotta love rubber floor mat ) but i cleared that issue when i checked all relays ,fused etc.. has anyone had this issue with there superduty ? Any spots where harness is known to rub thru on the fender or body ? Just thought i would check before i start unwrapping the wireharness. Thanks in advance for any help.

  • #2
    rig light problems

    First and for most i might not have understood but have you tried to ground the lights if you have power?. I have a GTC FF310 for these problems letting me trace wires in trucks from fuse box back and I Would consider looking into one it also shows open and broken circuits. I know on some fords inbetween 99 and 03 it is not uncommon for the cab marker lights to leak and drip down to behind the fusebox under the driver side dash and cause funny problems. I have seen them short out and cause draws and all kinds of other problems. I recommend trying to just trace wires it is a huge pain in the ass especially without specialty tools but is normally the only solution when power is lost somewhere in the middle of the truck. I might not have understood at all but I hope that helps
    Never Satisfied

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    • #3
      I ain't no Ford guy but I've done vehicle wiring as a hobby & professionally for a lot of years, so.... I assume you have a schematic from having done previous work on the loom. First thing I'd do is check continuity on the particular fuse for tail & marker, regardless of how it looks, or replace it anyway. Then check to see that you indeed have voltage coming to the input side of fuse, and check the output side of fuse for voltage.

      Then check a couple of the bulb housings to see if there's voltage where the bulb contacts touch. Here I would use a long jumper wire to a remote area like the engine block or battery negative for an auxiliary ground when testing bulb contacts. I've found over the years that at least 50% and more like 75% of electrical problems are due to bad grounds. Also with so much plastic and stuff used nowadays there's no telling what's used to ground devices compared to a good old fashioned all steel vehicle. You may then test between your bulb housings and auxiliary ground for continuity, preferably with power off so you don't accidently smoke your meter.

      If these tests show all is in good order regarding continuity, voltage and grounds I'd suspect some screwy problem that's computer related if not the main switch. All the best to you in your search! I love doing electrical especially custom work and building trick looms and vehicle mods, but troubleshooting can drive me absolutely bonkers somethimes...


      • #4
        I will have to agree with the guys above that mentioned bad grounds. Having been an electronics tech, having messed with cars and motorcycles and having built harnesses for custom vehicles, I'd say that before proceeding to do ANYTHING else, be sure that there is a good ground to the failed units. A lot of times the lack of ground will be not obvious because of things like connectors, vibration isolators, lifted grounds, etc....etc. My advice would be to string a separate ground line temporarily....use anything...(welding leads, jumper cables, a good piece of wire...****, even a chunk of ROMEX!) but just to be sure, check continuity of your temporary wire before doing any more testing. You just may be surprised! Any test rig must be KNOWN TO BE GOOD before you use it, or you will be getting false input (to your brain) and it will just make things even harder to figure out. Proceed step by step by step, checking everything including your test setup as you go.

        One thing to keep in mind is that electricity and wiring is all the same, no matter if it is in a Boeing 747, a John Deere tractor or a Ford truck!! Just use your head and use good, sound trouble shooting and you WILL PREVAIL!!

        I could tell you some (now) funny stories about chasing problems that turned out to be bad grounds, but I will refrain!

        Sometimes while working on a problem like that, I wil have a knowledgeable buddy take a look, too. It happens that a guy can overlook the most obvious stuff and having a second set of eyes and a second mind checking it out can be amazingly helpful. More than once I have thought.."NO ****...I never even considered THAT (in retrospect, something stupidly obvious) and guess what it turned out to be......!?!?!?"

        Oh, yeah...GOOD LUCK!!
        Last edited by dondlhmn; 01-20-2013, 08:54 AM.
        Don J
        Reno, NV

        Never pick a fight with an old guy. Old guys are too smart to fight and get hurt. They'll just kill you and get it over with.


        • #5
          I had the fuse box out and apart. All looked good. My brake lights and turn signals are on the same ground and they working good. As much as i hate to do it i gotta pull the wire harness and look for a broke wire


          • #6
            Yeh im testing them. I put my finger on it and see if i get shocked. I have voltmeters and test lights and know how to use them when i say eveything looks good it means the the little light came on. I am aware of how auto electric works. My post was asking if it was a common problem for the wire harness rubbing thru at a certain place or a wire issue that was a common ford superduty problem. This is not directed to all that replied. Just the 1 that thinks i stare at my truck to fix it