How to fix the headlights on my '72 Volvo ASAP?

August 28, 2004 2:23 PM

My headlights are out! [M to the Izzo]

I have a 1972 Volvo, and as of last night my headlights won't go on. All the other lights work, and none of the fuses I can see are blown. The alternator is working and the battery has a good charge. All the garages around here are closed for the weekend, but I have a multimeter and tools and I want to go to the rock show tonight! Unfortunately I know fuck-all about auto electrics. Can anyone give me a clue where to start checking?

posted by nicwolff to travel & transportation (10 comments total)

Nicwolf - The basic methodology is to start with what you know is the problem, and veify that it's the problem.

Off the top of my head, I'd guess a little bit called a relay is the bit that isn't working. But more on that in a sec.

So take that handy-dandy multimeter, figure out if the headlights themselves (test both of them) are getting current (if you have a wiring diagram for your car, this would help.) ... usually you'll want to test the wires that aren't green. Green *usually* means ground. Don't bet on that, as it's an informal standard.

Then test backwards from there. Trace the wires back to their next connection, and see if they're getting current on each side of that connection. And so on. When you find a spot where there's juice on one side but not on the headlight side, the bit that's in between is what's busted.

My guess, though, is that a relay ... like a remote switch ... is what isn't working in your case. If that's the case, start working on a friend to drive you, unless you happen to have a handy-dandy auto parts store nearby and they have one in stock!
posted by SpecialK at 2:32 PM on August 28, 2004

If you've checked fuses, battery and all else, you may just need new bulbs. Headlight bulbs are replaceable, and often burn out at the same time. Check to see if they work when you turn the high beams on. If so, it means that the normal-brightness filaments may have burned out. You can drive with the high beams only but you'll annoy pretty much everyone. See if an auto parts store sells replacement headlights and, with a screwdriver and a little bit of know-how, you should be able to replace them yourself. Here is some Volvo-specific advice for models somewhat later than yours. The only other electrical part to check is the headlight relay [which looks like this] which is more of a replaceable part than a fixable part.
posted by jessamyn at 2:43 PM on August 28, 2004

Ha! Thanks, jess - the high beams work, so I guess it's probably the bulbs. I wonder why they both blow at once though? I was assuming since it was both sides that it couldn't possibly be the bulbs, so duh on me.

So, I'll either borrow a (much less cool) car, or drive the back roads with the high beams a-blazin' - but in either case I can stop worrying about being stranded for days while the 1800 sits at the garage getting some electrical fault traced.
posted by nicwolff at 3:38 PM on August 28, 2004

Oh, and thanks too SpecialK!
posted by nicwolff at 3:41 PM on August 28, 2004

I was just going to suggest it was the bulbs as well. My father had this happen to him at least once and he went crazy trying to figure out what was wrong before he considered the possibility of both bulbs having burnt out simultaneously.

I think we also had both our regular water level light (the light that comes on when the water tank is full) and the backup burn out at the same time. Needless to say we had a couple of messy (and expensive!) deliveries from the water truck.

Yay serendipity!
posted by ODiV at 5:03 PM on August 28, 2004

SpecialK's analysis makes more sense to me. It's certainly possible that both bulbs let go at the same time (they are well-engineered to have a certain life) but using a meter to check for current at the bulb socket is free and easy.
posted by trharlan at 9:21 PM on August 28, 2004

If you want to check if the bulbs are dead or not, disconnect them, put your multimeter probe on them, and set your meter to ohms. If you get a reading of anything reasonable (oh, say, under 1k Ohm) then the filament isn't open and you *probably* have a good bulb.
posted by shepd at 10:09 PM on August 28, 2004

Well since there's still interest: after trying the high beams a couple times, the low beams are now working again! So at this point I'm figuring I have a faulty relay.

And the show was great: a band from Boston called "The So-And-Sos" that rocked with an agreeable hardness, and then Kay Hanley (former front-woman of Letters to Cleo) with her excellent current band. She's got one of the great pop-rock voices. But she should stop closing her shows with "Cruel to be Kind"! Some of her own stuff is great, but Nick Lowe was one of the great rock songwriters and ending with his best song just highlights the meh-ness of her weaker numbers.
posted by nicwolff at 10:18 PM on August 28, 2004

And thanks, shepd.
posted by nicwolff at 10:19 PM on August 28, 2004

Hey, no problem. :-)
posted by shepd at 2:38 AM on August 29, 2004