For the 1992 928GTS model:

Function   Wattage    Specification    Format Socket 
Headlight  60/55 W Headlight bulb H4 1R + 1R Ρ 43 t-38 
Aux driving lights  55 W Headlight bulb Η 3 YC PK 22 s 
Rear fog light with back light  21/4 W Twin filament ECE-R 37 BAZ 15 d 
Side- and additional indicator lights  4 W  Side light bulb  Τ 8/4 (HL)  ΒΑ 9 s
Back light & side marker lights  5 W  Round bulb  R 19/5 (G)  BA 15 s 
Number plate light  5 W  Soffit bulb 42mm C 11/L  SV 8.5-8 
Interior and luggage compartment lights, footwell lights  10 W  Soffit bulb 42mm C 11/K  SV 8.5-8 
Glove compartment light  3 W  Soffit bulb 28mm C 11  SV 7-8 
Indicator, brake, reversing light  21 W   Single filament  Ρ 25-1 (RL) BA 15 s
Engine compartment light  10 W  Round bulb (the GTS has a Soffit SV8.5-8)  R 19/10 (G) BA 15 s 
Cigarette lighter  2 W  Instrument bulb  J  BA 7 s 
Illumination switch lights, clock  1.2 W  Instrument bulb   WT5/1.2  W 2x4.6 d
Combination instrument illumination (warning) 1.2 W  Socket bulb 90 mA    T5
Combination instrument illumination  1.5 W  Socket bulb 110 mA     
Combination instrument illumination  2 W  Socket bulb 150 mA  wedge T10
Door guard lights  2 W  Side light bulb  Τ 8/2 (H)  BA 9 s 

Bulbs.xls

Some bulb dimensions ad styles:

BA15s  BA7s BA9s  PK22s

 

P43t SV8,5 W2x4,6 BAZ15

BA15d  BA15s  Sv7-8

Sv 8.5-8 mini T5