I bought a tail light that came with a bracket to mount the light on my seatpost. Trouble is, my seatpost only extends about 2 inches from the seat tube and I have an under seat wedge (bag) that fits in the same area. Is there an auxillary bracket available that would attach to the seat post and extend downward (under the seat bag) to provide a clear mounting location for my tailight? Any other options other that returning the light (and/or bag or bike) and starting over? — Thanks!

Most seat wedge bags that I'm familiar with have a horizontal strap across the back to accommodate rear tail lights via a clip. Would that work?

You can also try mounting the light on your left seat stay, assuming you don't have a rack in the way. This puts the light lower to the ground, which may make it harder to see, but also angles it up towards the drivers' eyes, so it probably evens out.

The problem I have with clipping most lights to most wedge bags is that the light often ends up sagging and pointing towards the ground.

I don't know of any brackets explicitly made for this purpose, though Topeak makes a seatpost bracket designed to mount a water bottle or one of its wedge packs. You might be able to modify this to clear your wedge pack and hold the light. Here's a picture of the Topeak gadget:

Topeak S.P.P. Fixer (http://www.bike24.net/images/products/p045862.jpg)

Most seat wedge bags that I'm familiar with have a horizontal strap across the back to accommodate rear tail lights via a clip.

This is kind of a minimal bag and I was surprised to find that, although there is a logo panel stitched to the back and a stitched reflective panel, there is no provision on the back to attach a light. :mad:

Also, the seat stays are carbon and have a shape (cross section) that will not accommodate the clamp supplied with the light. :(

The bike is my daughters Trek 2100 WSD. I have some photos and can post them (temporarily) at:

http://home.comcast.net/~kjzacharias/2100a.jpg
http://home.comcast.net/~kjzacharias/2100b.jpg
http://home.comcast.net/~kjzacharias/2100c.jpg
http://home.comcast.net/~kjzacharias/2100d.jpg

http://www.treefortbikes.com/137_333222336916__TL-1000-Rear-Light.html
Received one of these for Christmas.
It came with the seat post mount and a clamp for a frame mount that goes to the rear wheel.
It is BRIGHT.
Fred

Most seat wedge bags that I'm familiar with have a horizontal strap across the back to accommodate rear tail lights via a clip. Would that work?

Most of the blinkie straps on the seatbags I've seen always dangle the blinkie pointing down towards the ground this making the effective hot spots not pointed at the drivers so they don't detect a bike till they're close to you. At 80kph the car can come up every close from a distance away without seeing you till nearly two bus lengths away.

I use a short peace of PVC plumbing pipe with a 1/4-20 bolt, nut, and fender washers clamped to the reflector tab on my rack. The blinkie is clamped to the PVC pipe just as it would to the seat post. I had to cut an angle on each end of the pipe corresponding to the standard angle of the seat post as the notches in the blinkie clamp would not allow the blinkie to be properly angled. This had the added benefit of lowering the blinkie so items strapped to the top of the rack would not hit the top of the blinkie. This photo should answer all questions.
http://i143.photobucket.com/albums/r154/n4zou/Hpim0354.jpg

A power drill and assorted plumbing and cabinet hardware should be all you need to whip up a custom bracket.

I agree,
these bag straps are either useless or even dangerous because the lights will ending up pointing in whatever directions - Good mounting arrangements for tail lights are a problem.

Thanks n4zou for your suggestion! Are there any more such ideas ?

Most of the blinkie straps on the seatbags I've seen always dangle the blinkie pointing down towards the ground this making the effective hot spots not pointed at the drivers so they don't detect a bike till they're close to you. At 80kph the car can come up every close from a distance away without seeing you till nearly two bus lengths away.

What about a minoura space bar mounted to the seatpost?

Although, It looks like thats a carbon fiber seatpost, so at the very least, I'd want to make sure that any metal clamp would be well padded, so it didn't cut into the carbon fiber (or better yet, pick up an aluminum seatpost)