Day I dread follow up and taillight issue

Discussion in 'General Motoring' started by Jim Corey, Apr 4, 2005.

  1. Jim Corey

    Jim Corey Guest

    As I posted earlier, my 86 740 GLE, which I've owned since new, (350k miles)
    was rear ended. From insurance standpoint, totaled. After much back and
    forth, got enough to repaint the car (only MAACO), and buy a porta-power to
    do the body work prior to painting. (And to cover the costs of replacement
    taillights both sides, which I had on the shelf from an earlier e-bay
    purchase). About six hours work for son-in-law and I, and we were done. Car
    is finished, and looks quite nice.

    However, the car failed state light inspection (required when reregistering
    a "totaled" car). The brake-taillights, passenger side, where intermittent.
    No problem, thinks I. Probably too hasty in my reinstallation following the
    painting. After 2 hours, I couldn't isolate a ghost ground. The brake
    lights were grounding through the taillights. After fighting the problem, I
    threw a diode in the taillight lead, and VIOLA!!, problem solved.

    So now Victoria, our 740, will be good for another 350k (or at least outlast
    our S80!!)>
     
    Jim Corey, Apr 4, 2005
    #1
  2. Jim Corey

    James Sweet Guest

    Maaco paint turned out looking nice? That's a shocker, I've heard nothing
    but horror stories about them. Paint is one area where I absolutely will not
    cut corners, a cheap job that turns out crappy or doesn't hold up well will
    only cost more in the long run to clean up and repaint than using good paint
    in the first place.
     
    James Sweet, Apr 4, 2005
    #2
  3. Jim Corey

    Rob Guenther Guest

    Run dedicated ground wires for each light then, if you can... I've looked at
    the taillights on my 960 maybe twice, and I didn't get a good look at how
    the power rails were done, but it looked like it was possible from what I
    can remember... A 960 wagon has the same taillights as a 740, so it should
    be similar. I remember metal posts, where spade connectors could just plug
    right into (had to fix the taps for our trailers wiring harness...
    indicators weren't working, one lead fell off after 11 years) - you might
    have to cut the common negative rail, if there is one... Check connections,
    and check for appropriate signals from the positive wires first though,
    could just be a bad connection. (Check for a constant 12V for the running
    lights, a flashing 12V for the turn signal, a solid 12V for the brakes, when
    applied, a solid 12V for the reverse, when in gear, and a solid 12V for the
    fog lamp/s when on).

    I wouldn't use a diode to prevent a problem like that - because it means
    there is an actual problem with the wiring - Sounds like one wire is
    damaged, so the current is tracking back thru another one of your lights to
    find a path to "ground" (there's no real ground on a car... it's all direct
    current... positive and negative... Volvo's should be chassis <ground>
    negative)
     
    Rob Guenther, Apr 5, 2005
    #3
  4. Jim Corey

    James Sweet Guest


    In a 740 sedan (is this a sedan or a wagon?) the taillights ground with a
    ground lug stuck on one of the studs that holds the taillights in. Oxidation
    here is common with an old car, it's certainly possible to ground each light
    straight to a point on the frame inside the trunk or you can get some of
    those washers that bite into the metal a bit to improve the connection. The
    plug and connector where all the wires plug in is a bit of a weak spot too.
     
    James Sweet, Apr 5, 2005
    #4
  5. Jim Corey

    Rob Guenther Guest

    Those are some good idea's (washers, cleaning the plug connectors).

    Dirt and corrosion aren't good conductors, so i'd eliminate those problems
    first... Usually it doesn't take much to fix an electrical problem.
     
    Rob Guenther, Apr 5, 2005
    #5
  6. Jim Corey

    Jim Corey Guest

    Thanks. I actually did the "normal" troubleshooting (i.e. cleaned
    connections, etc.). I even swapped out the wire membrane on the taillight
    assembly. After 2 1/2 hours, I took the coward's way out, and did the
    work-around with the diode.

    Thanks for the tips.
     
    Jim Corey, Apr 7, 2005
    #6
  7. Jim Corey

    Rob Guenther Guest

    At least it's a clever solution that took knowledge of electricity :).
     
    Rob Guenther, Apr 8, 2005
    #7
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