Why is there a double filament bulb (1157) in the tail light socket? There are two spade connectors with wires connected to them but only one wire is hot when parking or tail lights are on. I'm also getting a "bulb out" warning light on the dash when I step on brakes but all three brake light bulbs are functioning? TD

 

the bulb out sensor gets fussy. get some deoxit, put it on all the connectors on both sides, use a bit of it to clean the contacts of the bulb sockets, etc. use matching bulbs on the two sides... use the chrome euro bulbs, not the brass ones.

 

Thanks for the tips Pierce. I'm thinking this is akin to the grounding problems many "old
Volvos" have. Since they stay in service so much longer than other cars, they develop corrosion in places un-explored by the average mechanic. I just didn't think my '93 has reached that age yet! Does the Bulb sensing circuit have something to do with the tail-light bulb having a double filament? I can't see any reason for two filaments since even with one burned out, both the parking-light & the tail-lights all work.

 

Double filament is because the bulb is used for brake lights and tail lights. One filament for each.

 

I think there's a few places where they used a double filament bulb but only used one of the two filaments.

 

I doubt the double filament is intended as a brake light as act1292 suggested, because I have a brake light, 3rd bulb up in the lens assembly. I suspect my wagon may be in the group that has a double filament bulb but only uses one. Is there anyway to check that out for sure?

 

look at the wiring diagrams for your year/model...

 

Will do. Main thing is, all the lights are now working correctly!

But here's another strange electrical anomaly. Recently repaired horn button contacts in steering wheel thus had to remove airbag. All went well but when I was done, I noticed the wheel spline was one tooth off so I removed the wheel and corrected it. When I reinstalled the airbag this time the SRS light came on and stays on. Someone mentioned it happened because in my correcting the the steering wheel alignment I had turned on the key with the airbag disconnected. Does that sound plausible? If so, how can I correct it?

 

The extra filament is for your rear fog lights. it works off of the driving light switch that is located left of the steering column.switch it one way is driving lights the other is rear facing fog lights. Rear facing fog lights are so you can be seen from behind.

 

Thanks for the info. As is often the case I did discover this after much experimenting. At least that makes it more likely that I'll remember it!! TD