Troubleshooting Auto Tail Light

Discussion in 'General Electronics Chat' started by wkumtrider, Dec 16, 2010.

  1. wkumtrider

    Thread Starter Member

    Jun 3, 2009
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    Hello,

    I have a 2000 Dodge Dakota and noticed my tail light is out. The same bulb operates the tail, brake, and turn signal. The brake light and turn signal work, but the tail light does not. I replaced the bulb but that did not help, so I'm assuming its in the wiring, switch, etc. I have a Chiltons manual that has a wiring diagram of the rear lights but it is not very detailed. What is the best way to start troubleshooting? The socket for the bulb has three wires.

    Thanks for all input and help!
     
  2. #12

    Expert

    Nov 30, 2010
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    The tail light, being a non-flashed circuit, must be in parallel with the other tail light, sooo...the problem should be fairly close to the socket. In fact, it probably is the socket! If the socket is good, start tracing wires.

    Just last week I bought a wiring diagram for a Chevy for $15 and fixed a dead battery problem (current leak) in 35 minutes. Having the drawings makes a LOT of difference!
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    The bulb must also be inserted correctly. It is hard to do, but possible to put the bulb in - in such a way that only one terminal is connected. Check the insertion and fit of the bulb carefully. Put a small piece of emery cloth on your finger and clean the contacts if they look corroded.
     
  4. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    There are probably two filaments in the bulb. One is for the tail light and the other is for the brake and turn signal. The three wires you mention are: ground, tail light power, and brake/turn signal power. You can check the continuity of the filaments in the bulb with a DMM set on ohms or with a continuity tester. Or you can swap the bulbs in the two tail lights and see if the problem follows the bulb. The point of all this is to be absolutely sure that you are not dealing with a defective bulb in which the tail light filament is burned out.

    Then you can check the voltage in the bulb socket. Turn on your lights and use your DMM set to DC volts to check for 12vdc between the metal body of the bulb socket and each of the two contact points inside the socket. One should show 12 volts whenever the lights are on in the vehicle and the other should show 12 volts only when the brake pedal is pressed or the turn signal is flashing.

    If there is no 12 volts on the tail light contact, you will need to trace the wires back until you find the break in the wire or a defective switch.
     
  5. #12

    Expert

    Nov 30, 2010
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    I assumed you knew how to change a light bulb, or even try a known good bulb. Sorry if I got ahead of you.
     
  6. wkumtrider

    Thread Starter Member

    Jun 3, 2009
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    Thanks guys. As mentioned in the OP, I replaced the light with a new one, and the tail light still didn't work. I also swapped the bulbs from each side. The tail light that was not working in the defective side worked fine on the good side. I have ruled the bulb out, and I have replaced these bulbs in the past so I'm pretty sure I have it in correctly. So, I will check the socket to see if it is bad (although the turn signal and brake light work fine). I did mention too that the same bulb (dual filament) operates the tail, brake, and turn signal.

    Thanks for the advice!
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    Many cars have the tail lights on the trunk (boot?) lid. The guarantee expires in 3 years so the flexed wires break in 4 years.
    A mechanic won't simply fix the broken wires, he will replace the entire expensive wiring harness.
     
  8. wkumtrider

    Thread Starter Member

    Jun 3, 2009
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    I hear you audioguru. If I can find the problem I'll fix it myself. I've cut and spliced a few wires in my lifetime!
     
  9. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Since it's a pickup truck I'd look at the wiring from underneath the truck.
    Pickups have a bad habit of slinging mud and other junk up into the area where the wiring is.
    In the winter you can have a 5 lb chunk of ice hanging off the wiring, which can pull a conductor out of the plug. Typically there is a plug underneath the truck on the drivers side that connect all the tail light wiring to the main harness, check that. Also, has your wiring been modified for a trailer hitch, if so check where the splices, if any, are made.
     
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    http://www.amazon.com/Fluke-TEST-LEADS-NAILS-MT-8203-20/dp/B0001FS9DO

    These are the BEST test leads for troubleshooting automotive wiring. They are Fluke "Bed Of Nails" alligator clips that put either a large needle or a lot of tiny spikes through the insulation.

    These do not damage standard insulation too badly for just getting the voltage, when removed, the insulation "heals itself" pretty quickly. It makes finding the right wire out of 20 take a minute or two instead of an hour or two, and worth every penny of the $25 investment!

    They will work with about any DMM that takes the CAT-III shielded banana clip jacks.
     
  11. wkumtrider

    Thread Starter Member

    Jun 3, 2009
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    Thanks, I'll check this out.
     
  12. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    If you are in a hurry. a few minutes with a file held on a flat surface and the tip of a meter lead can be sharpened to a fine enough point for checking through insulation. As mentioned the insulation will heal itself
     
  13. BillB3857

    Senior Member

    Feb 28, 2009
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    I frequently hit the wife's sewing table and swipe a pair of straight pins to pierce insulation for measurements with minimal damage to the wires.
     
  14. someonesdad

    Senior Member

    Jul 7, 2009
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    These are often called Popper clips (a trademark of Mueller Electric) (some competitors call them telecom clips to avoid the trademarked name) and there are a variety of types. They're nice as a general-purpose set of leads around the electrical bench and working on cars. However, for puncturing the insulation of a wire, I like a more specialized tool. About 20 years ago I bought a Fluke-branded one (but they're made by Pomona) for $20, but it has paid for itself many times over. The part is a 5913 Pomona part number (that might be a pair; all you typically need is one though). Cal Test also sells a version for $22. They typically make it easier to penetrate the wire to the conductor. I have used them in places where it would be impossible to use any other tool (e.g., inside a chunk of steel tubing).
     
  15. wkumtrider

    Thread Starter Member

    Jun 3, 2009
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    Well I ended up getting a basic circuit tester with a sharp pointed probe. A light comes on if the wire/circuit has any flow. It looks like it is my bulb socket. The wires work but I can't get a light when I test the socket. I looked all over the web and I can't find a tail light socket (the local auto parts stores don't have them). Anyway, thanks for all the help.
     
  16. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Not knowing where you live, Autozone and Advance Auto parts both carry a line of parts sold under the brand name 'Help'. They have just about all the different types of bulb sockets available. If not in the store they can be had in a day or two from the warehouse. Many of the young kids working in the stores don't even realize the carry them, unless you ask about the Help brand.
     
  17. wkumtrider

    Thread Starter Member

    Jun 3, 2009
    14
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    Thanks, I'll check it out.
     
  18. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    I had something similar happen to me.

    The right front light started to turn off intermittently. Then stopped turning on at all. So I would have no low beam, but high beam is fine. The left front light working fine.

    Went to the Autozone, talked to people. Ok, so the light bulb has two filaments, one for low beam, one for high beam. I figure the filament for low beam broke. I got ready to pull the light bulb out.

    The back of the socket has rubber boot that goes over it to insulate it from weather. I pushed on it, then check the lights, the bloody thing came on. That was it so far. Have been working for months now and I spent almost a year driving with only one front light before.
     
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