Electrical: Side/Parking Light Bulb

[Angie]

I've not needed to change bulbs in all the years I've had the car but with MoT due I checked and saw the RH light was out. Oddly the bulb is a dual-filament one but the LH is single filament, and that's what the handbook says is correct. Is this a modification for some reason, though I can't think why. The fitting in the unit looks original but is it possible someone has fixed an incorrect bulb holder without altering the unit? Any ideas appreciated, otherwise I might need to buy a new complete side-light/flasher unit. Incidentally when I wobbled the bulb it lit briefly, and of course it's been working for several years anyway. I tried another twin filament bulb but that didn't work, very peculiar!

[Stephen Edwin]

I remember a previous thread where someone had single filament one side and double filament the other side. It might be a tad tricky to search for though.

Anyway, your sidelights have worked for years and that bulb lights if you adjust it in the holder. So, clean up that bulb bulb and holder ... and maintenance spray the springs that support the contacts ... hopefully that should be job done.

And re preventative lubrication, you could search for your own post I recall about a dialectic conversation.

.

[Angie]

Stephen, thank you, I've done a quick search and there are many threads dealing with this and related problems. It looks as if one of the units is incorrect as some models did indeed have twin filament parking-light bulbs. The only thing is which ones, I think it was probably earlier ones. I think I'll try a clean up, maybe check the earth connections, and see what can be achieved.

I suspect that if the other Stephen (stephend) had replied this thread might have become a debate on the influence of mid-twentieth century serialism on Volvo lighting design!

I don't remember about a preventative lubrication thread but I'll search for it.

[Stephen Edwin]

The thread mentioning lubrication for electrical contacts is one of your threads about your air mass meter. http://www.volvoforums.org.uk/showth...ight=dialectic In the first two pages we were given advice about using Vaseline, or even a specific dielectic grease. Which I had not heard of before. You commented, dialectic conversation or some such rather neat terminology.

Sounds like the wrong light unit but I hope that by cleaning up the contacts you can avoid spending for a replacement light unit.

[Angie]

Problem sort-of resolved. I think that in fiddling about with the bulb with the lights switched on I probably caused the fuse to blow! I replaced the bulb, lights off, and all is well, so yes, it does appear that it must be the wrong fitting but it must be wired correctly. Sometime I'll buy a replacement unit but for now I'll just leave it all alone!

[stephend]

Angie, I think the trick is to look at the connectors, as they're part of the wiring loom and thus likely to be original. If the wiring is suitable for twin-filament (and the twin filament bulb operates at different brightnesses according to the headlamp switch position, as is the case on my 740), then the single filament bulb-holder is not original - and vice versa.

I don't know if the connector is compatible with both types of bulb holder, but I assume it must be, if that's how yours is connected?

I assume you know that the bulbs are slightly different in relation to whether the bayonet fitting is symmetric or not?

(In this instance, even I can't think of a Second Viennese School tangent to divert down!)

[Clifford Pope]

As long as you get the right kind of bulb for the holder then you can make use of either filament depending on how the wiring is connected to the holder. A 21/5w double filament bulb will obviously work in place of a single 5w one if wired appropriately.
Both variations have been used, depending on the model age, and the specific kind of driving light, dim/dip, sidelights on all the time, system used.

Just don't try and force the wrong kind of bulb into the socket, because the contacts for one/two lead blobs will obviously be in different positions, and the prong offsets are different. If you succeed in making the 21w filament work in a circuit meant for a 5w then the light will be too bright and it might well overload the circuit.

[Angie]

Originally Posted by Clifford Pope

As long as you get the right kind of bulb for the holder then you can make use of either filament depending on how the wiring is connected to the holder. A 21/5w double filament bulb will obviously work in place of a single 5w one if wired appropriately.
Both variations have been used, depending on the model age, and the specific kind of driving light, dim/dip, sidelights on all the time, system used.

Just don't try and force the wrong kind of bulb into the socket, because the contacts for one/two lead blobs will obviously be in different positions, and the prong offsets are different. If you succeed in making the 21w filament work in a circuit meant for a 5w then the light will be too bright and it might well overload the circuit.

Thank you, Clifford. I think whoever fitted the incorrect replacement unit must have known what they were doing because the 5 watt filament lights. My car has dim-dip, so presumably the single filament on the left is the correct fitting. Anyway I'm relieved that I haven't needed to source a new unit before the MoT on Monday.

[Clifford Pope]

That's right - dim/dip only has the single filament bulb. I've been tempted to use a double unit once myself, converting the wiring, as I happened to have a spare unit. Externally they are identical.

Some people don't like the dim/dip, so you can if preferred just disconnect it, perhaps replacing the 5w with a 10w to give brighter all-day sidelights instead.

[Michael J]

My '89 DL has 21/5W DRL/park lights and dim-dip. It depends on the model year.