(bulb out) indicator light problem

Hello to fellow volvo owners and enthusiasts. I've viewed this group
often....lots of great info. I own a 89' 740 and I'm having a problem
with the bulb out indicator light located in the speedo display. With
headlights on, it stays on, if I put the high beams on, it goes off. All
bulbs are working(I've checked every bulb and connection multiple times).
This all started with a recent low beam headlight being replaced. I can
live with the idiot light staying on, but it only serves to remind me
that I might BE an idiot, since I can't solve a seemingly simple
problem. I tried a second headlight, in case the first was somehow
faulty, same problem. Any input would be greatly appreciated.

TIA,

MW

 

problem. I tried a second headlight, in case the first was somehow faulty,

My 2 cents....
I think the reason might be that after replacing one bulb you have two bulbs
with different wattages now. Either check on the bulbs that they have the same
watt number or check by removing the second old bulb and put in two identical
new ones.

Viktor

 

Viktor=Victory! It's fixed! I took the second new headlight and put it
on the other side....bingo! Man, you just made my day. Thanks for
posting, I really appreciate it! I always thought these non-specialty
headlghts were generic/universal to replace. So I've learned something
new today. Thanks again, Viktor!

 

The bulb failure sensor is super sensitive, even bulbs aged differently
will sometimes trigger it. Replace them in pairs and you should have no
trouble.

 

That also explains why the lamp went out on high beam. High beam is used much
less time than low beam. So the current it draws is still very close to the
current a new bulb. The low beam is on permanently, at least in many European
countries, so it has aged a lot.
Viktor

 

Yes, I will do this from now on. Plus, at least theoretically, the new
bulbs of same manufacture should have , more or less , the same
lifespan. Though, I guess, some parts fail prematurely. But since bulbs
are relatively inexpensive, this is a good idea. Thanks, James

I kind of understood that it was a current problem, because of the high
beam causing the lamp to go out. The thing is, I was leaning towards
faulty wiring or even maybe a relay or something. I really would not
have ever thought of the uneven current from the bulbs themselves. Sorry
to get a little silly with the victory thing, but this problem had me
vexed, on and off, for a number of days. When I was able to just change
the bulb....well, I know it's a simple thing, but I was pretty happy.
Appreciate you guys sharing your knowledge. Thanks!

 

They normally do. What I do is replace the pair, then keep the remaining
good one in the car as a spare. That way if one burns out, I can pop
that in to get me by until I can make it to the store.

 

The bulb failure sensor does not monitor the high beam lamps, it only
looks at bulbs that are considered critical.

Really I'm not sure why they bothered monitoring the headlights, you can
easily tell if one is out. The sensor is very handy for the tail lights
though since you can't see those.

 

James, I'll be keeping the extra headlight I replaced, good idea. You
know, I noticed the high beam wires branch off from the low beam (four
headlight system). Just curious, how does the sensor exclude the high
beams in this case. Would there have to be a direct connection by the
sensor to the high beams? Why do you think the sensor light would go out
when the high beams were enabled?
MW

 

Pick up a Haynes manual and look at the schematic, that will answer your
questions. The high and low beams share a common ground and the wires
are all bundled into one harness but there's two separate circuits and
only the hot leads to the low beams run through the bulb failure sensor.
When you switch on the high beams, the low beam filaments in the outer
lamps shut off and the high beam filaments come on instead along with
the inner aux high beam lamps.

 

I've seen these manuals at the local auto parts store. Although you've
pretty much answered my question, I think I'll pick one up. Appreciate
it, James
MW