Pre-facelift rear light clusters
 

So we've been a Volvo family for some time and in the past 30 years between myself, mother, father and sister we have had: 240, 740, 850, 440, 480, V70 (2), XC70 (2), XC60 (2), S40, V40, V50 (2), C70 (2), C30, V60 and XC90.

My point is that all of them - except the XC90 - have 2 bulbs in each rear light cluster for the position (side) light. Why Volvo decided to put only one in the XC90 when there's loads of room - I don't know why. It's a really useful feature, a single bulb fails but you are still safe and legal.

Anyhow I removed the nearside rear cluster on my XC90 this weekend to dry it out as it had condensation in it and to investigate whether I could replace the brake light bulb with a twin filament 21/5w lamp to create a second position lamp. That's going to need some modification as the lamp holders have difference bases so you can't get them in the wrong holes - but I noticed that the side lamp itself is already a twin filament 21/4w lamp - but why? And why only 4w not 5w?? The brake and fog lamps are separate - what is the 21w filament used for?

It's of no real consequence but if anyone has any ideas... I'm really curious.

Hi,

I think I remember the answer to this one from the past.

Volvo fitted exactly the same lamp cluster to XC90 pre facelift irrespective of which market they were being supplied to. The side/marker position contains a twin filament bulb on both sides.

European legislation requires a high intensity rear fog lamp to be a minimum of 100mm from a brake light, hence why we have the rear fog lamp in the bumper on the driver's side and the opposite fog 'lamp' is just a blank reflector assembly. The main rear lamp cluster just isn't big enough to meet the 100mm rule.

America is different, from memory on a USA spec car the side marker lamp also becomes the rear fog lamp when activated, hence the twin 4w/21w bulb, and both of the reflectors in the rear bumper are dummy lamps with no wiring to them.

I imagine that the wiring or module control for lighting is different in USA & some other markets, illuminating the 21w filament when the fog lamp switch is activated.

No doubt someone will tell us I'm wrong, but that was my understanding when I delved into it years ago!

Paul

Paul's response, is the same as my understanding for the twin filament bulb.

I have recently had some issues with brake lamps blowing and was considering trying to rig something up to use these bulbs as extra brake lights?

Andy

Thanks Paul - I know you're right as I remember the 100mm rule (now you have reminded me) from when I used to build trailers...

What I'm thinking of doing now is swapping the twin filament bulb into the brake light aperture and vice versa - but replacing the single filament bulb with a 5w. That gets me 2 position lights on each side....

Thanks again.

I'm surprised no 3rd party created any rear lights for these as they're longest running shape next to Lada