Light Bulb Replacements
By Scott Mueller.

I have done some research on the bulbs, and have already upgraded or changed virtually ALL of the bulbs in my car! Here is what I found out.

The factory installs the following bulbs for the following applications:
Taillamp 2057
Backup 2057
Front Cornering 2057
Front Park/Turn 2057NA
CHMSL  2357 (Center High Mounted Stop Lamp)
Rear Side Marker 194
Rear License Plate 194
Ashtray 168
Glovebox  194
Rear Roof Rail   192 (Rear reading lights)
Instrument cluster PC194 (Instrument cluster background illumination)
Warning/Indicator PC161   (Instrument cluster warning lights)

What is interesting is that although there are several different numbers listed for the above two sets of applications, all of those listed above comprise basically two different kinds of bulbs! What I mean is that all of the bulbs in the first group plug into exactly the same socket and have exactly the same dimensional specifications, and likewise for the bulbs in the latter group. Since many different numbered bulbs interchange in these two types of sockets (even more than are listed above), I set out to find what the differences were between these different numbered but physically similar bulbs.

All of the bulbs in the first group, which comprise the tail and backup lamps, Center High Mounted Stop Lamp (CHMSL), front park/turn signal as well as the cornering lamps are technically classified as a type S-8 bulb with a DC (Double Contact) index (staggered pin) base, dual C-6 (straight across bar type helical coil) filaments, and a 1.250" LCL (Light Center Length = distance from the base to the filaments). These bulbs are about 1.041" (26.44mm) maximum diameter and 2.0" (50.8mm) in overall length. There are several bulbs with these exact same specifications, however they differ in the light output or wattage of each filament, and in some cases the average filament life.

There are several bulbs which meet the S-8 specification, and which are interchangeable in an automobile application:

Trade No Filament Volts Watts Amps CP Life
2057 Low 14.0 6.86 0.49 2 5000
High 12.8 26.88 2.10 32 1200
1034 Low 14.0 8.26 0.59 3 5000
High 12.8 23.04 1.80 32 200
1157 Low 14.0 8.26 0.59 3 5000
High 12.8 26.88 2.10 32 1200
2397 Low 14.0 6.72 0.48 2 5000
High 12.8 28.54 2.23 40 400
2357 Low 14.0 8.26 0.59 3 5000
High 12.8 28.54 2.23 40 400
CP = Candle Power

This data was taken from a Wagner Lamp Specification Guide, other brand bulbs may vary slightly in specs, but not by much. As you can see from this table, I have listed the bulbs roughly in order from dimmest to brightest. For example, comparing the 2057 that comes in the stock Impala taillight with an 1157 replacement, you can see that they are essentially the same bulb, except the 1157 would be 50% brighter on the low (parking light) filament.

I have gone the next step and installed 2357 bulbs in my taillights, backup lights, and cornering lights, which are 50% brighter on the low filament (parking lights) and also 25% brighter on the high filament as well. This makes the brake lights, turn signals and cornering lights that much brighter. There is a slight tradeoff in bulb life, but 400 hours is the average life of a headlight bulb anyway, and brake lights and turn signals are not on continuously anyway. Note that the super bright 2357 bulb was already factory issue in the CHMSL.

Each one of these bulbs is also available in an "NA" version, which means the bulb is coated with a Natural Amber coating. For example, the stock Impala front park/turn signal bulbs are 2057NA, while I have replace mine with brighter (both in park and turn signal mode) 2357NA bulbs. Personally I feel that having brighter parking, stop, turn signal and cornering lights are an excellent safety feature, not to mention one of the easier mods you can do! Just one more thing to make your Impala stand out from the crowd.

Now how about the other group of lights? The Rear Side Marker, Rear License Plate, Ashtray, Rear Roof Rail (reading lamps), Instrument cluster, and Warning/Indicator lamps all use the same basic type of bulb. These are a T3-1/4 Wedge Base bulb, which is about 0.4" (10.3mm) in diameter and 0.81" (20.6mm) in overall length. There are several bulbs which meet this specification, and as such are interchangeable:

Trade No. Design Volts Watts Amps Avg. CP Life
161 14.0 2.66 0.19 1 4000
158 14.0 3.36 0.24 2 3000
194 14.0 3.78 0.27 2 2500
192 14.0 4.62 0.33 3 2000
168 14.0 4.90 0.35 3 1500

Note that the stock Impala rear side marker bulbs are the 194s, which are only 2 candle power just like the low filament of the 2057 taillamp bulbs.
So to maintain parity with the brighter 3 candle power parking light portion of the 2357 bulbs I installed, I changed the rear side markers to 168s, which match the 3 candle
power exactly. I also put the 50% brighter 168 bulb in my glove box, replacing the stock 194 factory installed bulb.

The instrument cluster uses a variation of the wedge bulb. They are mounted in a twist lock base that plugs directly into the printed circuit board on the back of the cluster. When sold with the base, these are called PCxxx bulbs, for example a PC194 is basically a 194 bulb that comes soldered into a PC (Printed Circuit) board twist lock base. Older GM cars (around '90 and earlier) used a standard bulb which would plug into a separately available twist lock base, allowing you to easily change the bulb since you could re-use the base. The newer ones have the bulb permanently soldered into the base, so when one burns out you have to try and find the special PCxxx version rather than just replace the bulb in the existing base.

If you are going to change your instrument cluster bulbs to brighter ones, I suggest you just get the separate PC wedge bulb base, then you can use any one of the non-PC standard T3 1/4 wedge base bulbs by just plugging them in. You can get the correct stand-alone PC wedge bulb base from GM under p/n 25015169. What I did was to use that base and install a conventional 168 wedge bulb which lights up the background numerals and needles much brighter. If you want you can also replace some of the warning indicators with brighter bulbs also, that way when they light up you can't miss them. I always think about the Tim Allen joke about his wife seizing the engine after the oil light came on... "You mean you drove the car after the light came on?", "I thought if it was REALLY important it would have been brighter or something."

BTW, I hope you can find the answer to your question in here somewhere.

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