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S80 low beam, harness severe heat damage, have replaced, fails again S80 2001

posted by  timbales on  Tue Jun 19 15:16 CST 2012
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last visit: Tue Jun 19 15:07 CST 2012
[RELATED]

Dipped Beam failure is the error prompt I believe ( son's car ). We've found info describing the SHUNT ( resistor ) having a poor/carboned/burnt connection to the CEM. We pulled the CEM down to examine and all shunts are fine, no telltale heat damage on CEM or on any shunts or relays. The damage to the drivers side low beam harness is profound. Ceramic remains, and plastic insulation melted away. Burn your car down level damage.
So, with no problem evident at the shunt on the CEM, what recommendations does my esteemed audience have. I mean "help me" please :-)

Can the shunt be 'bad' and have no visible damage?

Can we ohm out the shunt to see if it is okay?

Which, shunt is the dipped beam shunt?

Should I use one of the other, identical shunts, on the board, walking the problem, perhaps elsewhere?

Thanks guys, I appreciate any help you can throw at this.

Tim Bales







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    posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

    As you said, the shunt appears to be OK. Have you lost both low beams or just the one side? You might be in need of a new ceramic plug. If there are pick&pull yards around, just cut the wires off a good looking S80 and replace yours???

    Also, get your alternator checked, you do not want it putting out more than 14.5V
    --
    My name is Klaus and I am a V ♂ lv ♂ holic



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      posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

      Thanks for follow up.

      Stepping in for my father here on the thread...

      I have only lost the ONE driver side (left) low beam.

      We ultimately ended up replacing the headlamp plug, again. I say again because the original factory plug had similar heat damage/degradation, and so we replaced it about 2-3 months ago with an aftermarket ceramic wiring harness/plug (this product: http://www.amazon.com/Hipro-Power-Ceramic-Headlight-Harness/dp/B005J6YUY2). We cut off old/original plug, spliced and soldered this one in.

      Much to our surprise - the aftermarket plug got cooked. Melted the plastic shell covering the ceramic plug. The wires feeding in to the plug melted off part of their sheath. Pretty aggressive levels of heat & damage for the headlight!

      So, in reverting to my father's original post - we checked the shunts, fuses, did a visual (cursory) inspection of the wiring under the hood, CEM looked fine, etc. - everything looked good.

      Alas, as I noted above we gave up and just spliced in another ceramic aftermarket plug. I'm monitoring it now for similar failure - so far it's holding up, but seems substantially hotter than the other headlight.

      And that is key here: the other headlight (passenger/right) side is just fine. Original factory plug, no problems.

      We wished to fix the cause of the problem, but we just replaced the plug again - anticipating a repeat of before.

      So if it's just the one headlight, does it make sense to check the alternator?

      Is it possible that the headlight relay (is there more than one?) is bad and is affecting just ONE headlight?

      Any and all ideas appreciated!

      Thanks,

      Greg Bales


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        posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

        There is only one relay, located on the side of the dash and #3 from the bottom, right hand column:
        http://www.matthewsvolvosite.com/downloads/2001_S80_2001_S70_wiring_diagram.pdf

        So, the factory plug lasted for 10 years and the 'new' part for 3 months? With all of the junk yards around, you should be able to get OEM for cheap. I wonder what the dealer would charge?

        You also need to verify that the bulbs are the same output. This is a 14.4V system, which is why I suggested to stop by an autoparts store and verify that the voltage is under 15V.

        Those wires look like 16 gauge? Are they solid copper or braided, braided will cause more resistance - heat.
        --
        My name is Klaus and I am a V♂lv♂holic



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