All the credit for this wiring diagram, goes to ig88vsbobafett http://www.fiero.nl/forum/Forum1/HTML/058885.html
Cavalier	Fiero
C1 connector is left side of Cavalier cluster
C1-1 Ign Power Pnk/Blk	C2-9 Ign power Pnk/Blk
C1-2 SES Light Brn/white	C3-10 SES Light Brn/Wht
C1-3 Seatbelt light (power for 5 secs) Yellow	C3-8 Seat Belt light Yellow
C1-4 Ground/blk	C2-4 Ground Blk
C1-5 Shift light	Not Used
C1-6 Not Used	Not Used
C1-7 Tach Imput Wht	C3-18 Tach Imput WHT
C1-8 Ign Power from fuse Pnk/blk	Splice from C2-9
C1-9 Ground/blk	Splice from C2-4
C1-10 Speed sig. Out to ecm	C1-U VSS to Cruise and ECM Drk green/Wht
C1-11 Speed sig. Out to cruise	C1-U VSS to Cruise and ECM Drk green/Wht
C1-12 Not Used	Not Used
C1-13 Not Used	Not Used
C1-14 Not Used	Not Used
C1-15 Not Used	Not Used
C1-16 Brake Light Tan/Wht	C3-14 Brake LT Tan/Wht
C1-17 Low Collant	Not used on the fiero
C1-18 Ign Power from fuse Pnk/Blk -	C1-T Ign Power to cluster Yel/Blk
C2 connector is right side of Cavalier cluster
C2-1 Ground/Blk	C3-11 Ground Blk
C2-2 Ground/Blk	C3-11 Ground Blk
C2-3 Ign Power Pnk/Blk	C3-9 Ign power/ fues Pnk/Blk
C2-4 Ign Power Pnk/Blk	C3-9 Ign power/ fues Pnk/Blk
C2-5 Collant Temp Drk/Grn	C3-13 Coolant Temp Ind. Drk Green
C2-6 Oil Pressure Tan	C3-17 Oil Pressure guage Tan
C2-7 Fuel guage Pink	C3-7 Fuel Guage Pnk
C2-8 Outside Temp Tan	PinB outisde temp Pnk/Wht
C2-9 VSS Gound Blk	C1-R Vss Low Ppl/Wht and PinA outside temp Pnk/Blk
C2-10 Dim Display BRN	C3-3 Panel Illumination Gray
C2-11 LH Turn Lt Blue	C3-2 LH Turn LT/Blue
C2-12 RH Turn Drk Blue	C3-4 RH Turn Drk Blue
C2-13 High Beam Lt Grn	C3-12 High Beam Lt Green
C2-14 Illumion Battery voltage Gray	C2-12 Panel illumination input Gray
C2-15 Battery Power from fuse (Controls Trip)	Wire to fuse box (hot at all times or you will lose the trip)
C2-16 Not Used	Not Used
C2-17 Not Used	Not Used
C2-18 VSS Imput Yellow	C1-S VSS High Yellow