I agree.  Control is directed by what circuit is jumped from - brake or tail....brightness is controlled by bulb wattage.  I update the blank lens to another taillight bulb which, given the lens configuration, is more less a bright color reflector but gives light when viewed off center from the rear of vehicle....it's a fair upgrade for taillights.  I would not recommend using this to add another brake light as the lens pattern really distorts at higher wattage and there is no mirror reflector in that blank so it's really a washed out light pattern.  Here is a link to one of my vans (4 sale) with a pic of the update-scroll towards bottom of page.

http://members.fortunecity.com/planetp/89Vanagon.html

I run 12 watt bulbs for taillights and 50 watt halogen for brake lights, the difference is hard to miss and clean reflectors help as well.

JB

-----Original Message-----
From: Matthew [mailto:poll7356@uidaho.edu]
Sent: Tuesday, December 23, 2003 3:43 PM
To: Birkenfeld Jeff; vanagon@GERRY.VANAGON.COM
Subject: Re: Tail light update

yikes! this concerns me because the tail lights are too bright wrt to 
the brake lights. You *need* a big difference in the tail light and 
brake lights so the guy behind you can see the brake lights!  Don't 
believe me? Follow someone with lights that are not well differentiated 
and you'll know exactly what i mean.

> http://www.weirdstuffwemake.com/automotive/vanagon/pics/misc/NewBusTailLights.jpg