(Before and After pics. Of the original Fiero wire harness)
This is the one item that I have had the most questions from prospective customers. Many can't understand how they can still use the stock harness with the V-8 swap. Others who are going to use Fuel injection have questions on how we go about "Piggy-Backing" the computers. This subject is covered in detail in our Video Instruction Tape but I will try to give enough detail here to answer most questions. We will divide this subject into 2 parts You first need to understand that if you are using a Fuel Injected engine you will need to do almost all the Carbureted wiring then, in addition, you will do the supplemental Fuel Injection wiring. So the 2 subjects for this item are: 1) Wiring for Carbureted applications. And 2) Supplemental wiring for Fuel Injected applications.
1) Wiring for Carbureted applications:
When using a carbureted engine the following items from the original Harness are NOT used and the wires and connectors can be removed from the original harness or moved to a position that is safely out of the way.
A) All connections to the original Fiero fuel injection system, including fuel injector or throttle body connections, cold start injector, MAP sensor, TPS sensor, O2 sensor,
B) All ignition system wires except the Pink "Hot with ignition on" wire and the White "tach" wire.
C) All water Temp. Sensors except the Sensor for the Water Temperature Gage.
If you are unsure of the elimination of any wires you can use this method. As stated earlier we will continue to use the original oil pressure sender, water temp. Gage sensor, A/C compressor, Alternator, speed sender, backup light connections, Torque converter lock up connection, along with the Pink and White Coil wires, we will also still use the "Purple" wire that went to the original starter solenoid. All wires in the original harness that go to sensors or connectors that are still on the original engine are wires that we will not be using.
Of all the wires we keep, they all go to the original destinations or connectors if these original destinations or connectors are still used in the new engine/trans./cradle/chassis assembly. In addition the "Purple" starter wire goes to the small terminal on the new starter. The "Pink" coil wire goes to the "Batt" terminal on the new distributer or coil. The "White" coil wire goes to the "Coil" terminal on the new distributer or the "-" terminal on the new coil.
NOTE: the "Pink" & "White" wires are the only one that go to a different destination with TPI than with Carburation, see below.
2) Supplemental wiring for Fuel Injected applications.
Now on this car we are also installing a TPI Fuel Injection system. In this type of installation we need to use the original type TPI computer to control the engine functions. I, personally, am not the least bit interested in automotive wiring even as a hobby so I always use and "Aftermarket" TPI wiring harness when using fuel injection. You will find that there are many, many, and many more companies that offer "Aftermarket" wiring harnesses for the "Street Rod" and "Hot Rod" industries. You'll find that the SBC TPI Injection systems are very popular for use in other industries and that wire harnesses for these engines are very easy to find. If you were doing say a 3.8 swap (or many other types of swaps) into a Fiero, you can be sure that you will be almost totally on your own on obtaining help building an appropriate harness. On this car we are using a harness that we obtained from Street & Performance, This harness will work out to be a "Plug and Play" type deal, it is so simple to use that is it worth the price. In our case for the TPI to be able to handle the ZZ4 engine we also needed a set of the 24# LT1 injectors. We choose S & P as our supplier for two reasons, I have had good customer support from them and most of all they had the LT1 injectors at the best price. You can also get harnesses from Ron Frances Wire works or Dr. K's or any number of other suppliers that would probably work just as well.
On the TPI system once we have wired the engine as we would for a carbureted engine we need to install the "Aftermarket" wire harness. It comes with all the proper GM connectors and all the wires are labeled as to exactly where to plug them in. In addition the "Aftermarket" wire harness has 6 wires that are labeled and we need to connect those into the original Fiero Wire harness, this process is what I call "Piggy Back". These 6 wires are as follows:
1) "Hot with ignition on" this wire connects to the "Pink" wire from the original Fiero harness.
Tach." This wire connects to the "White" wire from the original Fiero harness
to Starter Terminal" This wire goes to a hot all the time source.
Engine Ground" To Engine Ground
Fuel Pump" This wire goes to the Fiero fuel pump Hot wire. So that the new computer controls the fuel pump.
VSS Vehicle Speed Sensor" wires splice these right into the "Purple" and "Yellow" wires in the original harness that go to the original Fiero speed sending unit.
There are also a few other wires included with the "Aftermarket" harness that you can use to connect to "Aftermarket" gages if you want to, these are optional and not required when doing the TPI into Fiero swap.
That's all....It's very simple if you address the "Aftermarket" harness one connection at a time.
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