Here is a gauge cluster pinout, written by Whiskey River, a user of w-body.com forums. Hope it helps. The base cluster is if you have the 85 mph speedometer, and the pinout below it (Gauges cluster) is for the 115 mph speedometer/tachometer gauge cluster. Good luck.
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"Sorry this took so long. My phone line was dead over the weekend. Here goes. If you are looking at the connector, clip at the top. The top row is C, bottom row is D and they go 1-16, left to right.
For the Base Cluster
C3 - Pink/Black - Ignition Power
C4 - Yellow/Black - Low Coolant Light
C5 - Tan/White - Brake Light (parking brake or low brake fluid)
C6 - Brown -Charge Indicator
C7 - Dark Green - Coolant Temp Indicator
C9 - Black - Ground
C10 - Brn/Wht - SES Light
C11 - Tan/Blk - Shift Light
C12 - Lt Grn/Blk - Antilock light (if so equipped)
C13 - PPL - Fuel Level indicator
C16 - Lt Blue - Left Turn signal
D1 - tan - Oil Pressure Indicator
D2 - Yellow - Fasten Seat Belts Indicator
D8 - Gray - Dimmer switch
D12 - Black - Ground
D13 - Dk Grn - Speedometer
D15 - Dk Blue - Right turn signal
D16 - Lt Grn - High Beams
Ok, here is the pinout for the gages cluster.
C2 - Black - Ground
C3 - Gray - Dimmer
C5 - PPL - Fuel Level
C7 - Dk Grn - Coolant Temp
C9 - Lt Blue - Left Turn Signal
C11 - Yellow - Fasten Seat Belts Ind
C13 - Tan - Oil Pressure Indicator
C15 - Brn - Charge Indicator
C16 - Yel/Blk - Low Coolant
D1 - Dk Blue - RH Turn Signal
D2 - Lt Grn - High Beams
D3 - Tan/Blk - Shift Indicator
D4 - Pnk/Blk - Ignition Power
D5 - Dk Grn - Speedometer
D6 - Black - Ground
D9 - White - Tach Wire
D11 - Pink/Blk - Ignition Power
D13 - Tan/Wht - Brake indicator
D15 - Lt Grn/Blk - Antilock indicator
D16 - Brn/Wht - SES Light.
Wow, that was long, ok, for the two power wires, you have to choices, run a new lead from the fuse box to the second power lead, or run a jumper from one to the other. Which is what I did. As for the tach wire, you will need to get under the hood and unplug the left connector on the ICM. There are 5 wires in that connector. They are:
Tan/Blk - Bypass Wire for ECM
White - Tach signal for ECM
White - Tach signal for Instrument Cluster
PPL/Wht - Reference signal for ECM
Black/Rd - Ground from ICM to ECM.
You will need to splice into the white wire that is next to the purple wire. If you tap into the wrong one, it may cause the car to act up as the ECM won't know how fast the engine is running."