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Both Highbeam Filaments Blown

Help, Advice, Owners' Discussion and DIY Tutorials on all Volvo's "mid era" rear wheel drive Volvos.

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thatvolvonut
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Joined: Tue Aug 06, 2019 6:45 pm
Year and Model: 1992 240
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thatvolvonut

Both Highbeam Filaments Blown

Post by thatvolvonut » Tue Aug 06, 2019 7:10 pm

Hi guys, I'm completely baffled by this one. Having just pulled out of my driveway I turned on my high beams and boom - I got a bright flash and then inky darkness. I was scared that my step relay had finally given up the ghost but I get a nice loud click out of it and the high beam indicator on the dash still functions. I do have the signal lead for a relay for a pair of 55W driving lights hooked into the dashboard indicator light, but the wire running to the headlights themselves is untouched. I took the bulbs out and, lo and behold, both high beam filaments are blown right out. They're both blown in exactly the same place and in the same way - the connector between the curly part of the filament and the support wire just turned into a blob on the inside of the glass. I've never seen anything like it; I think (hope?) it was just a fluke but I figured I'd ask before I blow 2 brand new bulbs.

For those of you who like TL;DR lists:
- 1992 base 240, USDM
- 1 pair of 55W halogen driving lights wired as follows: junction block -> 40A relay contact -> lights -> gnd, dashboard high beam indicator -> switch (OEM A/C switch with bulb) -> 40A relay coil -> gnd
- high beams cycled on and off a few times (I believe the driving lights were on during this)
- tried to cycle again, got a bright flash and they both went out at the same time (I'm pretty sure the driving lights were still on)
- low beams still work, though I noticed just before this happened that the left headlight connector was a little flaky (pulling it out to the limit of the clip broke the connection)
- both high beam filaments are blown in the same way
- the driving lights and dashboard indicator still work as expected, and the step relay clicks normally when toggling high beams

The diagrams don't show any fuses in the circuit, so the headlights appear to have acted like the fuses! What could have caused this? Relay weirdness? Flaky connections (though wouldn't that just reduce the power to the lights)? Cosmic ray burst?

Thanks!



thatvolvonut
Posts: 2
Joined: Tue Aug 06, 2019 6:45 pm
Year and Model: 1992 240
Location: NH
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thatvolvonut

Re: Both Highbeam Filaments Blown

Post by thatvolvonut » Fri Aug 16, 2019 5:53 pm

Just wanted to post what I think is the solution - I was on my way back from Team O'Neil's RallyFest with my mom when the alternator completely gave out! My dad picked up an alternator and came to the rescue and I made it the rest of the way home without incident. I don't know if the two incidents are related, but everything is working now.



lummert
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Joined: Tue Jan 29, 2008 5:39 pm
Year and Model: 760 1988
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lummert

Re: Both Highbeam Filaments Blown

Post by lummert » Fri Aug 16, 2019 8:42 pm

An alternator that is overcharging can blow bulbs as well as many other issues.


1988 Volvo 760 Turbo Wagon

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