I am look for something to provide hints on how to build the harness. Or some step my step instructions. If not here are some questions.

It looks like the original 3800 harness is designed to go to the Fiero trunk side of the engine. So if I want to mount the PCM in the interior the wires will need to re-routed. How best to do this? I assume it would be best to run the wire under the SC snout to keep them way from the exhaust. Picture would help.

What technique are being used to shorten the wiring? Are mechanical crimps being used or are you soldering the wiring.

What heat shrink tubing class is being used (e.g., low temperature <200 or high temperature >200.) If using high temperature heat shrink where are you getting it?

What materials are being use to wrap the harness? Is it the split plastic tubing, spiral wrap or tape? Is this low or high temperature material? What are you sources?

Are you building the harness with the engine in or out of the car? Are there any critical dimensions for locating the PCM in the stock locations?

To shorten the harness are you just cutting the harness or working it wire but wire?

Suggestions for gourmets for bring the harness through the firewall.

Thanks

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88 GT 5 Speed Black with gray interior

I disassemble the entire harness, remove all the wires from the PCM, label each group of wires at the PCM end.

Then i start connecting them to the engine with it in the car and find the best/cleanest way to route them. mark where grounds will be,the PCM will be and so on. tape them at all the branch points so it can all be removed and kept organized. Then lay it out on a table and start putting the wires where they need to go in the PCM,c500 and c203.

If wires need shortened I re pin them, and if they need lengthened I use solder and high temp shrink. The pins and shrink tube I get at a local manufactures overstock electronics "junkyard" in town.

I tape wrap the entire harness to keep the wires organized and suggest people to use quality split loom on it. Sometimes I will add the foil heat shield wrap near exhaust parts if needed.

There are good instructions on Ryans site at GMtuners.com under technical/download wiring diagrams and pinouts

Here are a ton of build threads. I am sure there is wiring info in here but where exactly idk

https://www.fiero.nl/forum/Forum2/HTML/079560.html

I personally would never use metal crimps. I hate hate hate having to troubleshoot troubles caused by short cuts. Metal crimps WILL fail over ime.
Solder or run the wires all the way to the end. Some people use crimp on inserts for the connector ends. It would be like popping out the metal insert of the connector, putting one on a new wire or wire from the old harness, and then usually soldering them to make sure they don't fail.

If you make a bunch of solder splices, make them staggered in the wiring harness. That way you don't have the snake that swallowed a rat look to your 'factory' harness.

I think you could build the harness in or out of the car. For a beginner I would think you would get a better job doing it in the car so your lenghts are correct. Avoid any temptation of making the wires too long. Make them the exact lenght you actually need.

Without a question you need to work the harness wire by wire. Some of the wires go to C500. Some go to the ECM. Some go to C203. Start by marking the connectors on the 3800 harness. Cut the harness with more than enough tail on the ECM end. Then seperate the harness to the connectors. Make circles out of the wire from each connector. Add a second tag to the other end of the wire coils.(Like a CAT 5 cord - about a 6" circle) Wire tie the wire circles so they are more managable to work with. Then with the engine in the bay route the wires from the connectors to where you need them to go. If you need to extend the wires keep the colors stock. Extra wire can be obtained from the old Fiero harness. If you need more than that 'harvest' a harness from a 3800 at the junk yard. That way you will have colors that match. As you route your wires tie them together with something again like wire bread bag ties so you can open them and close them again. After you have all the wires routed you can then encase them in whatever manner you like.

I have a bunch of wiring pics in my N/A swap thread. The wiring is the same NA or SC pretty much. Like others said, just go wire by wire and take your time.

https://www.fiero.nl/forum/Forum2/HTML/102326.html

best way is to remove all the pins from the pcm connectors and then run all your wiring were you need it and then you can reinstall the pins. This way you can do away with some of the wiring you do not need.

[This message has been edited by fierofan25 (edited 12-01-2010).]

What did you use to remove the pins from the connector. Is this a standard pin removal tool. Where did you get new pins for the connector. Can you get them at an auto part store or are they a dealer item? Do the pins come with a new seal?

When you remove the clear and blue covers off the PCM connectors you will see the little clips that hold them in. They are much easier to remove them most connector pins. Befor you star rebuilding the connectors write the word "BLUE" on one of them, there is no way to tell them apart once you take the covers off. I have a link somewhere of a place you can order pins, I will look for it and repost.

Thanks for the information. I figured out how to get the connector covers off and understand how to remove the pin now. Having the link to a source of the pins would be great.

Can the new PCM be mounted in the same location as the original ECM? It looks like it would be close. A bracket would have to be fabricated. Any suggestions?

I posted the pin links above. Yes the PCM can fit the stock location connecors on top, just cut away some of the bracket and velcro or zip tie it.

Thanks for the help. I will start next week by dissembling the wire harness including taking the wiring out of the connectors.

If I want to leave the battery in the stock location is there a preferred location for the coil pack? Some have installed them under the grills, however I live in the northwest and want to drive the car in the rain. I don’t think I want the grills drain on the coils.

I usually mount them on the firewall, some put them on the trunk wall. Yo can put them wherever you like really.