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Very odd brake/taillight problem

Well, it certainly seems odd to me. New VW Beetle (Turbo S if you care) and there is a problem with the left rear brake/tailight. With just the headlights on, the tailight is just fine (normal illumination, same as the other taillight). With the headlights off, the brake light works just fine (bright, same as the otehr brake light). But when the headlights are on, and the brakes are applied the left rear light goes completely off. Remove the brake and it goes back to normal taillight brightness.

So to recap: taillight alone is good, brake alone is good, brake and taillight together is no light.

When it was in this mode, I removed the taillight assembly and by the time I had it out and ready to be looked at, damn if it wasn't working correctly. Put it back in and it was good for a day or so, then back to bad.

Any ideas of where to look would be greatly appreciated.

-Jim

Reply to
Jim Wall
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If it changed back to working mode when you had the assembly out, I think its about a 99.99999% chance there's a loose connection between the wiring and the actual light bulb. Maybe the ground connection is loose, that is the common point where each filament would get connected back to the negative polarity, which is also the frame of the vehicle.

Either jump in with a voltmeter and measure what's going on in all states, or wiggle things around until you can figure out what's wrong.

Shouldn't be to hard as there's only a few wires there and very basic wiring involved.

GK

Reply to
George Kowal

Yep, the OP is almost certain to find this is indeed the problem. The taillamp filament is probably grounding through the brake lamp filaments in series and via the other-side brake lamp's ground path. When the taillamp is on, grounding in this fashion, and the brakes are applied, the brake filament goes from path-to-ground to +12V, therefore no more light.

Sounds crazy -- just like front sidemarkers wired across park-and-turn to burn steadily with lights on, flash in sync with turn signals with lights off and flash in opposite-phase with turn signals with lights on -- until you realize that to the 8w taillamp filament, the 27w brake lamp filament, or even two of them in series, look like a free and clear path to ground.

Another possibility, only somewhat less likely, is that an improper bulb has been installed. The one and only correct bulb (at least up to 2002, latest year of the Neobug covered by my weatherlies) is a P21/5W. That is Osram/Sylvania 7528, Narva 17916, Philips 12499 or direct equivalent. An American-type 1157 (2057, 2357, 1034...) will fit and light, but the wattages are wrong and the base is plain brass, which leads to FAST corrosion in sockets designed around the assumption of the ECE nickel-plated base.

I've seen even VW dealers cramming 1157s where P21/5Ws go...

DS

Reply to
Daniel J. Stern

Well, sure. They're cheaper and last longer.

nate

Reply to
Nate Nagel

Well, sure. They're cheaper and last longer.

nate

Reply to
Nate Nagel

Cheaper, yes. Last longer? Well, if they're one of the dwindling range of good-quality 1157s available, yes. A great many bulbs are being outsourced to e.g. China; reject percentages are soaring and quality is plummeting.

DS

Reply to
Daniel J. Stern

Actually even I have been known to use the 1157Ks in cars that didn't originally call for them. Those *do* have nickel plate bases. Reason being that I have a hard time getting an original-style flasher that works with 1034 bulbs. Haven't had one go on me yet, although the older cars that this is an issue for generally get driven infrequently and in nice weather (although I hope that's changing soon... almost got one project to the "potential daily driver" stage)

nate

Reply to
Nate Nagel

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