one burnt out DRL???

Bad bulbs. I don't know the 4-digit number of the DRL bulb in the current GM trucks, but it begins with a 3. The heavier replacement bulb begins with a 4 and has the same last three digits. Someone once told me that it has to do with the fact that the original bulbs when specified by GM were rated for

12v, but the truck's electrical system actually runs at 14+v, about a 20% increase over spec in voltage which was the cause for the shortened life span of the bulb.

Cheers - Jonathan

Thanks for the information Jonathan. It seems like every 00'+ Chevy truck I see on the road has one of the DRL's burned out and I have always wondered about this as well. Curiosity is finally answered..............

Doc

Well, Jonathan, I don't have a clue as to whether you're right or not. I bought my 99 and wanted to change my DRL's to amber. So, I pulled the stock

3157's and put in 4157na/LL. I've run them for 22 months and haven't had one burn out yet. I have changed one 3157 turn signal, and one 194 park/turn signal in the same period. Unfortunately, I also had one of my low beam silverstars go south on me. Dang it - they're expensive! I've got a bunch of extra lights on mine. Some are LED's and some are clearance type lights. The worst light on my truck is the high mount 3rd brake light. It works ok, but it is so chincy(?) it looks like they went into the back alleys in Taiwan to find the cheapest POS that has ever been invented. Its the all-time worst design and I hope the guy lost his job over that one.

a 4157 is a heavy duty bulb. N/A is the code for Amber. LL is the code for Long Life.

I have replaced 3157 N/A's (3157kNA) with 3457 N/A's (3457NAk) before and not had an issue. Just like replacing 161's with 194's.

Charles Bendig

Thanks, Charles! I knew that!

Anybody know why the DRL bulbs are dual filament bulbs? I can't figure out any function of the second filament. Are both filaments on during DRL operation?

It's for the flash-to-pass operation in the day time. When you pull the turn signal knob back toward you the second filament turns on and makes it brighter like brake light bulbs do.

Aha, you learn something everyday. That has been bugging me for a while. I thought the flash-to-pass only turned on the high beams briefly. Let me ask you this then; if my DRL is burned out, can I remove the bulb and flip it over so that the burned filament is for the flass to pass and the good one is the DRL?

I don't think it will flip over. The bulb has 2 pins on the side where you stick it in and give it a half twist to lock it in, one is closer to the glass than the other so it only fits in 1 way.

No, that's not how the bulbs go it at all. The are not quarter turn bulbs. You can flib the bulb over and put it in, I'm just not sure if that will switch the filaments.

It will flip the filaments; then the drl won't work. I missed the thread where someone said it was for flash to pass. I have a 99 silverado - my flash to pass turns off the drl and flashes the high beam. If you have something like a cavalier or a saturn, it uses a reduced voltage to the high beam. So if you flash to pass, it applies full voltage which makes it the actual high beam.

OK then, Tell us what the dual filament bulbs are for.

I think George is agreeing with you, Williams. He is just saying that you can indeed flip the bulb over and switch the filaments. Which I personally think is a pretty neat trick since those bulbs burn out about every 6-9 months. At least their life can be extended sort of. I saw in a different thread that there was a heavy duty version of the same bulb that should last longer. There are also LED replacements that probably last about forever but they would have to to justify the price. They are like $16 if my memory serves.