Bad ground. What is happening is that the brake light circuit is trying to use the hot side of the parking light circuit as a ground instead of the sheet metal of the car. With the parking AND brake filaments lit, you've got 12V from the former running head-on into 12V from the latter. Like two matching forces pushing directly against each other, the result is zero volts, which is why the bulb goes out. With the park lights off, the brake light can no longer use it as a path to ground and must use the obviously degraded (ie: corroded) factory ground that you have -- which is why it is so dim.
A better analogy would be a tee intersection, with two cars (one being the power from the brake circuit and one for the park circuit) moving directly towards each other, and the tee (the ground path) much too heavily congested for both cars to use simultaneously. Take out the second car and there's just enough room for one of the cars to turn down the side, but not without a lot of scraping (resistance) going on. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Rob Garretson Sent: February-14-10 12:27 PM To: [email protected] Subject: [vintagvw] 67 tail light help Hi, I have a 67 bug with a problem tail light. It is the right hand side and here is what is happening; Press brakes = light works, but is not as bright as the left side Headlights on = all is good Headlights on and press brakes = light goes out Both rear turn signals work fine. I have checked and replaced the bulbs with no change. Any ideas? Thanks, Rob Garretson ☮ [email protected] [email protected] "Once in a while you get shown the light, in the strangest of places if you look at it right." Robert Hunter, Jerry Garcia _______________________________________________ vintagvw site list [email protected] http://lists.sjsu.edu/mailman/listinfo/vintagvw __________ Information from ESET Smart Security, version of virus signature database 4866 (20100214) __________ The message was checked by ESET Smart Security. http://www.eset.com _______________________________________________ vintagvw site list [email protected] http://lists.sjsu.edu/mailman/listinfo/vintagvw
