Re-wiring the Iron Duke engine bay... (Page 1/2)
82-T/A [At Work] NOV 18, 03:32 PM
So, in my daughter's 1985 Fiero 2m4 SE, I've noticed that the way the engine wiring harness was installed, I have to assume the reason it was done so is because the engine was provided as an assembled unit with everything already installed onto it at the Fiero plant. Meaning that the engine was likely built somewhere else, and everything was assembled as a complete unit, and all they had to do was plop it on the subframe, take the harness connector and plug it into the firewall.

As my daughter removed a lot of the wiring from the engine compartment, it seemed the most ridiculous was the harness that wraps along the front of the engine bay in that plastic shielding, which then goes to the A/C compressor. So I think it's safe to conclude that when they designed this, it was more ease of installation... and not necessarily what would be the most ideal wire routing. Has anyone (after rebuilding their engine and re-doing the engine compartment), re-routed some of the wiring, like for example, along the front firewall for things that otherwise don't need to be wrapped around the entire engine block?
jdv NOV 18, 05:03 PM
When I did my 3500 swap i rewired the engine bay and removed about 3 feet from the harness. Instead of coming out of the cabin and going toward the front of the engine it went toward the back by the transmission. This engine had duel exhaust that came down from the manifolds so there was no crossover. I had only a couple that went back the other way to the fusible links but there was no wires coming across by the water pump to the fusible links. Looked much cleaner. My car car was a v6 but same idea.
theogre NOV 19, 01:46 AM
Another think know better then GM Engineers... Worse another YT "show" wants more free help...

Duke wiring is Not just to make it easier to install.
For 1... Keeps most of wiring Far Away from the Exhaust. Wiring is Rated to handle engine heat otherwise.
2. The duke & others "loop" setup from ECM to C500 has the shortest wiring path for the FP AC Relays, many "ground" that some are Not Grounds, ECM Sensor wires, & way more. Example: The Distributor & TBI has wires to ECM & C500. While Alt has wires to C500 & Power "box" under that.
3. The "loop" has enough Slack to allow the engine to move & often even when have iffy engine/trans mounts & dogbone won't rip out the wiring.
4. if you need to pull the engine, For Fiero, you only need to discon C500, ECM, C203 & Maybe a few other plugs then drop the whole assembly out the bottom w/ the wiring. Ignoring rust frozen hardware, this can be done in Hours to get out then again to get in. And if you're careful you don't need wheel alignment if problems are in engine &or trans. & you don't mess w/ AC except to unbolt the compressor from mounts.
5. You can get to nearly all engine plugs/ends to easily test whatever even for OP sender to switch to 88 Plug to follow FSM directions to find most problems. + now you can get DC Amp Clamps & more tools to find a problem w/o cutting the wires etc. to test.

E2A--->
The AC compressor wires need a relay to work. So where are you going to mount that? There is no space near the battery for it or FP Relay. So if you put AC limit switches & Clutch wires, Clutch that pulls 7-10a even more, to go on firewall then have more wiring for the clutch not less when snaking around the battery to get to C500 that may need bigger "pins" to handle Clutch power.

IOW GM route all AC to C203 & ECM plugs so all go thru same path so Relay mounts in cooler area & no looking for other ECM wires going thru C500.
Because ECM has Final Control of AC because will turn the Compressor Off @ various conditions. 1 input line is you wanting AC & all limits are closed. 1 "output" actually turns On the Clutch Relay then that turn On the Clutch coil.

Go & look @ AC wiring in FSM Alldata etc that proves what I've said.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 11-19-2023).]

82-T/A [At Work] NOV 19, 11:23 AM

quote
Originally posted by theogre:

Another think know better then GM Engineers... Worse another YT "show" wants more free help...

Duke wiring is Not just to make it easier to install.
For 1... Keeps most of wiring Far Away from the Exhaust. Wiring is Rated to handle engine heat otherwise.
2. The duke & others "loop" setup from ECM to C500 has the shortest wiring path for the FP AC Relays, many "ground" that some are Not Grounds, ECM Sensor wires, & way more. Example: The Distributor & TBI has wires to ECM & C500. While Alt has wires to C500 & Power "box" under that.
3. The "loop" has enough Slack to allow the engine to move & often even when have iffy engine/trans mounts & dogbone won't rip out the wiring.
4. if you need to pull the engine, For Fiero, you only need to discon C500, ECM, C203 & Maybe a few other plugs then drop the whole assembly out the bottom w/ the wiring. Ignoring rust frozen hardware, this can be done in Hours to get out then again to get in. And if you're careful you don't need wheel alignment if problems are in engine &or trans. & you don't mess w/ AC except to unbolt the compressor from mounts.
5. You can get to nearly all engine plugs/ends to easily test whatever even for OP sender to switch to 88 Plug to follow FSM directions to find most problems. + now you can get DC Amp Clamps & more tools to find a problem w/o cutting the wires etc. to test.

E2A--->
The AC compressor wires need a relay to work. So where are you going to mount that? There is no space near the battery for it or FP Relay. So if you put AC limit switches & Clutch wires, Clutch that pulls 7-10a even more, to go on firewall then have more wiring for the clutch not less when snaking around the battery to get to C500 that may need bigger "pins" to handle Clutch power.

IOW GM route all AC to C203 & ECM plugs so all go thru same path so Relay mounts in cooler area & no looking for other ECM wires going thru C500.
Because ECM has Final Control of AC because will turn the Compressor Off @ various conditions. 1 input line is you wanting AC & all limits are closed. 1 "output" actually turns On the Clutch Relay then that turn On the Clutch coil.

Go & look @ AC wiring in FSM Alldata etc that proves what I've said.




Hi Ogre, I think you're making a lot of assumptions here. Several of my wife's friends from UF ended up working for General Motors as mechanical, electrical, and space engineers. It's well-known that the routing of most wiring harnesses and the way they're designed has a lot more to do with ease of installation during the assembly and manufacturing process, rather than it does for any optimal path consideration. It doesn't take an electrical engineer to understand that wrapping an entire wiring harness around the engine, literally hugging it to the engine, and wrapping it down the front of the motor, is not the most ideal placement for most wiring. I'm certainly not asking what I can cut and remove.


"Worse another YT "show" wants more free help..."

You probably could have left that out... it was rather snide. I'm not asking for "free help." I can absolutely figure this out myself, it's not difficult, I'm asking for ideas to see what others have done. I want to clean up the engine bay.
jdv NOV 19, 01:57 PM
Todd look over Fieroguru's ls4 thread to get some ideas as he does some incredible work on a fiero.
Raydar NOV 19, 04:25 PM

quote
Originally posted by theogre:

Another think know better then GM Engineers... Worse another YT "show" wants more free help...




Could you be any more condescending? I'm sure you could, if you tried.

Jeebus.

Todd, Just make sure the wiring - especially the battery cables - is routed away from hot exhaust, and moving parts (belts, pulleys, etc.)
I've done a couple of V6s. I wasn't too displeased with how the wiring was run, except that some of it had to be run before the accessory brackets and coolant pipes were installed.

[This message has been edited by Raydar (edited 11-19-2023).]

buddycraigg NOV 21, 04:14 AM
I never really questioned it.
I just assumed that they built the harness to accept any and all combinations of options for the engine.
theogre NOV 21, 03:41 PM

quote
Originally posted by Raydar:
Could you be any more condescending? I'm sure you could, if you tried.

You're just another sucker for this racket...
Oh gee, kid want to rebuilt X car. Better is a girl wants it. Then parent(s) was Free info & more & push the channel/"show" to get viewer # hope to get viral or @ lest to get monetized etc. Maybe even local news coverage because "girls don't to this" @ outlet wants "feel good story" that week. Then get free stuff from vendors too. He's already getting Free Ads spamming General w/ posts for every "episode" on YT.

We've seen this happen here w/ big thread starter 10+ years ago. Some saw the "writing on the way" was going dead very soon as other projects/programs & making "statues" to sell ate more & more time But they Never told anyone. Many still didn't get a clue when she left for whatever university several years later.

I've seen this same thing happen many times in other places even before YT having most "Car Restore" projects that are abandoned in similar ways but YT & Internet have these making money, free parts & more. If they abandon the car, the free parts often go on CL Ebay etc.
theogre NOV 21, 04:08 PM

quote
Originally posted by buddycraigg:
I never really questioned it.
I just assumed that they built the harness to accept any and all combinations of options for the engine.

Nope.
Just Fiero Duke have several engine wire harness for any given model year.
Big Obvious is different ones for Auto vs Stick Transmissions. I believe sub versions for AC vs no AC for each of those.

Cabin Wire harness has similar changes depending on Transmission & other Options. Example: AC vs no AC then entire heater "box" is way different & no AC = no Mode Motors & more & doesn't have AC control wires.

Some cases are Exceptions...
Like the Power Truck Release wiring is in the 86-88 cabin harness even when car don't have this option.
But Notch vs GT may have exact same Cabin harness because "programing" for the Taillight is done by 1 Jumper in C500 being there for notchies or missing for GT. Yes. 1 wire goes from the brake pedal switch to C500 & back to the turn light switch just "to see" which set of taillight.

Plus @ least 4 versions of "Taillights" harnesses... notch vs GT + cruise servo or not for each.

[This message has been edited by theogre (edited 11-21-2023).]

Dukesterpro NOV 21, 06:29 PM
Ogre, you got to chill out man.

You firmly believe the engineers know best. They don't always. I'm an engineer, I work in product development (electronics) for a extremely large company with products installed in almost every major building you have ever walked into since 1913. I know damn well that sometimes stuff is pushed out the door as a mother of necessity. Stop blasting everybody's ideas just cause they go against your philosophy of "that's not how the engineers did it." Especially when you're using the fiero as your guide for what the engineers intended. Every component of this car excluding the space frame and the panel construction absolutely reeks of rush job, cheap shortcuts and redundancy. Its just the nature of the beast. If we didn't have people who looks at something like that and went "Boy, i wonder if there's a better way to do this?" We'd still be riding horses without saddles.

You are attacking a member who simply wants to verify information before posting it to his daughters YouTube channel. Who gives damn if they are trying to grow the channel, the daughter seems to enjoy herself and its seemingly useful information. If the channel makes it 15 episodes and dies, what difference does it make? The daughter, a member of the youth you tend to criticize is attempting learning and trying to teach the tools and skills necessary to carry the torch your generation is leaving behind. As far as your diminutive statement of "wanting free information." its a forum guy, that's what they are for.

You aren't required to answer and support these things that your thrashing on. Even if your vast wealth of knowledge is appreciated and dont get me wrong, it is. It would almost be better that you don't answer if you are just going to tear everyone down while doing it.


Best thing you can do 82 T/A, if you are going to reroute, is keep focused on keeping wires as far from the heat as possible and as high up as possible, to make them easier to get to, and prevent hidden wires from causing faults later on. Maybe start with the OG harness and build a new one one wire at a time, routing each wire along there new path. Your gonna want to use heat resistant wire loom.