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low beam halogen voltage drops, what should they be? Topic is solved

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mrbrian200
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low beam halogen voltage drops, what should they be?

Post by mrbrian200 » Wed Jul 13, 2016 3:54 pm

I have noted my RH low beam occasionally flicks momentarily brighter by maybe 5-10%, just enough to notice..
LH low beam and both high beams unaffected.

Voltage drop between bulb to ground 0.1v
Voltage drop across connector behind headlamp assembly (+) side 0.0v
Voltage drop between bulb and F16 (wire + CEM) 0.5v

On the LEFT side the drop between bulb and F17 is 0.3v
But with approximately 4-6 feet of extra wire running to the RH side 14AWG @ 5A the longer wire run should explain the 0.2V difference between Left and Right. Or not?

Previous owner replaced the RH bulb pigtail, I'm not the first one to go after this. I soldered the wires they had just twisted together with black tape to rule that out.

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mrbrian200
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Re: low beam halogen voltage drops, what should they be?

Post by mrbrian200 » Thu Jul 21, 2016 2:31 pm

Is the manufacture date somewhere on the car or do you have to look that up by VIN/chassis?
New style CEM cover/grommet already installed, no sign of water intrusion whatsoever. But that was switched over during the '06 model year (might be original, might not). Various stickers none of them shows the actual date that I can tell.
I did unseat all the terminals in connector B and solder the wire crimps in the chance that the CEM was replaced but the connector was deemed ok with oxidation becoming a problem over extended time. Sprayed all terminals and pins with CRC electrical cleaner. Haven't done a long night drive to determine if that made any difference in that RH low beam occasional bright 'flick'. I probably shouldn't rule out the possibility of a faulty bulb. Bulb in that position when I bought the car was very dim by about 40% but might have just been a mismatch where previous owner didn't replace in pairs. New bulbs corrected the obvious low output on RH but this occasional bright 'flick' is something to worry about in my book. I don't need this drawing my attention when driving at night when I need my attention focused on the lookout for !!DEER!!.

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mrbrian200
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mrbrian200

Re: low beam halogen voltage drops, what should they be?

Post by mrbrian200 » Sun Jul 24, 2016 1:27 pm

That seems to have nailed it (unplugging CEM top connectors, soldering terminal wire crimps on connector "B"). I can now see that RH low beam had been re-aimed higher to compensate for a lower light output. Now that it's full bright it's obvious. I'm thinking galvanic corrosion at the crimp (copper wire to tin/steel terminal). I'm certain that is the issue with problematic battery wires/terminals in the trunk. On the firewall/load center end there's more to it (moisture/oils/salt brine wicking up the copper threads that aren't sealed up and causing the wire to rot from the inside out). This isn't a problem specific to Volvo. Nearly every car I've ever owned needs a round of electrical work at about this age to correct a funky issue or three. I prefer to repair rather than replace. Costs NIL and in many cases easier than snorting out/replacing an entire harness.

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mrbrian200
Posts: 1552
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mrbrian200

Re: low beam halogen voltage drops, what should they be?  Topic is solved

Post by mrbrian200 » Thu Feb 16, 2017 12:46 pm

Long term update on this. Prev post in July I was mistaken. The issue remained after soldering the wire crimps for the lob circuit through the CEM. The issue was intermittent and maybe a week after doing that (and posting) I noticed it again. Issue was finally resolved after soldering the terminal wire crimps along the CEM power feed wires from the trunk - all of them starting at the feed at the battery post through the fusable links (11/E), connectors 54-40D and the connector at the CEM. Pretty sure the problem was at the CEM connector as one of the terminals crimps showed slight discoloration at the terminal crimp that would be consistent with heat generated by a voltage drop. Though I did this several months ago and initially appeared to be a success, this time I decided to wait awhile to make sure. The main beams do not feed through that circuit this would indicate it was actually the city light(s) doing it. I don't feel too bad about the miss. PO replaced the main beam pigtail in a failed attempt to rectify, so I'm not the first one that barked up the wrong path. But I eventually got it.

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