Fiero C203 & C500
This is a list of all the connections that are needed to tie into the Fiero electrical system when doing an engine conversion. This list is to aide in the wiring process. All circuits should be verified before any connections are made. To the best of my knowledge, all of the info below is correct.
The C203 connector is clear plastic and located under the center console. The C500 connector is next to the battery, half of it is for the tail light harness, the other half for the engine. Descriptions of each one follows:
Fiero C203 connector
| Pos. | Wire color | Circuit | Description |
| A | Tan/Black | Upshift lamp | Grounding this wire will make the upshift indicator come on. |
| B | Orange | Fuel Pump | Positive feed for the fuel pump relay. Hot at all times fused 10A |
| C | Brown/White | SES lamp | Grounding this wire will make the "Service Engine Soon" indicator come on |
| D | Lt Blue | A/C on | Positive feed for the A/C compressor control relay coil. Hot when A/C is on. |
| E | Tan | Oil gage | Connect to oil pressure sender, 90 ohms at max pressure |
| F | Pink/Black | ECM Ign. | Positive feed for ECM. Hot in run, bulb test, or start. fused 10A. |
| G | Yellow | VSS high | VSS input to speedometer. Connect to magnetic VSS or converted 4000 PPM signal from ECM. Note 3 |
| H | Brown | VSS feed for ECM | Feeds buffered VSS signal to ECM when a magnetic VSS is connected to speedometer. Note 3 |
| J | Pink | TBI INJ1 | Positive feed for injector. Hot in run, bulb test, or start. fused 5A |
| K | Pink | TBI INJ2 | Positive feed for injector. Hot in run, bulb test, or start. fused 5A |
| L | Tan/White | Fuel pump | Positive side of fuel pump, gets connected to the COM terminal of the fuel pump relay. |
| M | Black | VSSB ground | Connect to ground |
| N | Black | A/C Power | Positive feed for A/C compressor control relay contacts. Fused 25A |
| P | Purple | TCC Brake switch | TCC brake. Hot in run, bulb test, or start only when brake pedal is NOT depressed. |
| R | Purple | VSS low | VSS input to speedometer. Connect to magnetic VSS or to ground if using optical VSS and converter. Note 3 |
Notes
1. F is the switched power feed for the ECM, all switched 12 volt inputs on the ECM can be
connected to this terminal. The constant 12 volt supply for the ECM comes from the rust
colored fusible link with a single weatherpack disconnect at the terminal block near the
battery.
2. J, & K are the positive feeds for the fuel injectors, One for each injector on TBI systems or one for each bank on PFI systems.
3. The Fiero speedometer system works differently than most other GM vehicles. Click HERE for more info.
Fiero C500 connector
I've found that the C500 connections vary considerably depending on
year.
| Pos. | Wire color | Circuit | Description |
| A2 | Black | Ground | Ground |
| A4 | Yellow | Start | Hot in start, connect to gear selector switch. Automatic only |
| B3 | Brown | Charge | Charge indicator light. Connect to alternator brown wire. |
| C1 | Dark Blue | Reverse | Reverse light switch power feed. Connect to gear selector switch(auto.) or reverse switch(man.) Fused 10A. Note 1 |
| C2 | DkGreen/White(V6) Tan(L4) |
Temp gage | Connect to temp sender, 1365ohm@100deg.,55ohm@260deg. |
| C3 | White | Tach | Connect to coil or ign module. |
| D1 | Dk Green/white | Fan switch | Connect to grounding fan switch or ECM fan output |
| D2 | Lt Green/Black | Fan switch | Same as above(with optional two speed fan only) |
| D3 | Dark Green | Temp lamp | Connect to grounding temp switch or ECM temp output. |
| E1 | Lt Green | Reverse | Connect to gear selector switch(auto.) or reverse switch(man.) along with C1. Note 1 |
| E2 | Purple | Start | Hot in start, connect to starter. Manual only |
| E3 | Pink | Ignition | Hot in run, bulb test, or start. Power feed for ignition coil |
Cars equipped with four speed manual transaxle use a shifter mounted reverse switch. Cars with five speed use a transaxle mounted switch. '85 and newer cars are wired for both switches.
There is a stud terminal directly under the C500 for making all +12 volt constant connections.
The Fiero uses a separate module for cruise control. It is located behind the carpet on the drivers side inner kick panel. If you wish to use the new donor ECM to control the cruise control (recommended), you will need to extend the wires from the original module to the new ECM.