Complete Bulb Chart + LED Conversion Guide
Platform: 1988–1998 Chevy / GMC C/K, Tahoe, Yukon, Suburban
This is the consolidated FSC master lighting reference for OBS trucks.
Built for restoration, troubleshooting, and full LED conversion builds.
OBS GENERATION BREAKDOWN (CRITICAL)
1988–1994 (Early OBS)
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Sealed-beam headlights standard (H6054)
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Early tail wiring carried over from squarebody era
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1988–1989 used 1157 / 1156 rear bulbs
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Slightly weaker factory headlight output
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Mixed interior bulb socket usage
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LED conversion slightly more involved
1995–1998 (Late OBS – Updated Front Clip)
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Composite headlights introduced (9005 / 9006)
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Rear lighting fully standardized to 3157 / 3156
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Improved marker + turn integration
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Interior lighting standardized to 194 / T10
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Easiest OBS years to convert to LED
Key Difference:
Rear lighting changed after ~1990 and is fully consistent 1995–1998.
EXTERIOR LIGHTING TECHPACK
HEADLIGHT SYSTEM
| Location | 88–94 | 95–98 |
|---|---|---|
| Sealed Beam | H6054 | H6054 |
| High Beam (Composite) | 9005 | 9005 |
| Low Beam (Composite) | 9006 | 9006 |
| Fog Lights | H3 | H3 |
Notes:
-
Relay harness upgrade highly recommended before LED swap.
-
LED sealed beams are direct replacement.
-
Composite housings benefit massively from proper grounding.
FRONT LIGHTING
| Function | Bulb |
|---|---|
| Front Turn Signal | 1157 |
| Parking Light | 1157 |
| Front Side Marker | 194 / T10 |
| Cornering Lamps (if equipped) | 3157 |
REAR LIGHTING
Early OBS (1988–1989)
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Tail / Brake: 1157
-
Reverse: 1156
1990–1998 (Standardized)
| Function | Bulb |
|---|---|
| Tail / Brake / Turn | 3157 |
| Reverse | 3156 |
| License Plate | 194 |
License plate bulbs unchanged across all OBS years.
CAB + MARKER LIGHTS
| Location | Bulb |
|---|---|
| Cab Roof Lights | 194 / 168 |
| Fender Markers | 194 |
| Rear Side Markers | 194 |
| Third Brake Light | 912 / 921 |
| Cargo Light | 921 |
INTERIOR LIGHTING TECHPACK
OBS interiors are largely standardized 1993+.
| Location | Bulb |
|---|---|
| Gauge Cluster | T5 or 194 |
| HVAC Controls | T5 |
| Ash Tray | 194 |
| Dome Light | 211-2 (41mm Festoon) |
| Map Lights | 194 |
| Glove Box | 194 |
| Stepwell / Courtesy | 194 or 211-2 |
LED CONVERSION STRATEGY (OBS-SPECIFIC)
Mandatory Upgrades
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Headlight relay harness
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LED-compatible flasher relay (prevents hyperflash)
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Ground refresh at radiator support + rear frame
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Inspect factory headlight switch (common failure point)
Known OBS Issues
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Factory headlight switch overheating
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Weak grounds
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Rear harness corrosion
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Inconsistent polarity on some circuits
Recommended Order
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Ground refresh
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Relay harness install
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Exterior LED swap
-
Interior LED conversion
COMPLETE LED SHOPPING CHECKLIST
Front
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2× Headlights (H6054 or 9005/9006 pair)
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2× Front turn 1157
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2× Parking 1157
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2× Marker 194
Rear
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2× Tail/Brake (3157 or 1157 early trucks)
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2× Reverse (3156 / 1156)
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2× Plate lights 194
Interior
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5–10× 194
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1× Dome 211-2
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Cluster T5 pack
OBS LIGHTING UPGRADE TIERS (FSC STANDARD)
Stage 1 — Restoration
OEM halogen replacements only.
Stage 2 — Modern Driver
Full exterior + interior LED conversion.
Stage 3 — Full OBS Retrofit
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LED housings
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Switchback front signals
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Smoked / clear lenses
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Sequential tails
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Relay harness + upgraded grounds
This TechPack will remain pinned in the GMT400 section.
If you find corrections, year-specific variations, or diesel differences, post them below so we can refine this into the definitive OBS lighting reference.