This comes directly from OSRAM SYLVANIA'S WEBSITE:
Auto Lamp Replacement Guide - Results
Print out the list and find them at your nearest retailer.
1988 FORD Mustang
High & low beam headlamp
9004
9004SU Silverstar ULTRA for Ultra Night Vision - The Whitest and Brightest Halogen
9004ST Silverstar High Performance Lighting: The Whiter and Brighter Halogen
9004XV XtraVision Halogen - The Brighter Light
9004CB Cool Blue Halogen - The Whiter Light
Parking light
1157A
1157AST Silverstar Signal Lighting: Complete the Look: Crisp, Clean, Style
1157ALL Long Life Upgrade: Up to twice the life of the standard lamp
Front turn signal
1157A
1157AST Silverstar Signal Lighting: Complete the Look: Crisp, Clean, Style
1157ALL Long Life Upgrade: Up to twice the life of the standard lamp
Rear turn signal
1156
1156LL Long Life Upgrade: Up to twice the life of the standard lamp
3157
3157LL Long Life Upgrade: Up to twice the life of the standard lamp
Tail light
3157
3157LL Long Life Upgrade: Up to twice the life of the standard lamp
Stop light
3157
3157LL Long Life Upgrade: Up to twice the life of the standard lamp
High mount stop light
912
912LL Long Life Upgrade: Up to twice the life of the standard lamp
921
921LL Long Life Upgrade: Up to twice the life of the standard lamp
Fog/Driving light
H3-55W
H3ST Silverstar High Performance Lighting: The Whiter and Brighter Halogen
License plate
168
168LL Long Life Upgrade: Up to twice the life of the standard lamp
Back up light
3156
3156LL Long Life Upgrade: Up to twice the life of the standard lamp
Front sidemarker
916NA
Rear sidemarker
194
194LL Long Life Upgrade: Up to twice the life of the standard lamp
Ash tray
161
Glove box
1816
Map light
105
Dome light
89
906
912
912LL Long Life Upgrade: Up to twice the life of the standard lamp
Step/Courtesy light
168
168LL Long Life Upgrade: Up to twice the life of the standard lamp
194
194LL Long Life Upgrade: Up to twice the life of the standard lamp
Trunk/Cargo area
98
Under hood light
98
Instrument-general
161
1816
1892
194
194LL Long Life Upgrade: Up to twice the life of the standard lamp
Hi-beam indicator
194
194LL Long Life Upgrade: Up to twice the life of the standard lamp
Seat belt indicator
194
194LL Long Life Upgrade: Up to twice the life of the standard lamp
Brake warning
194
194LL Long Life Upgrade: Up to twice the life of the standard lamp
Automatic transmission indicator
1816
Directional signal indicator
194
194LL Long Life Upgrade: Up to twice the life of the standard lamp
Radio dial
7152