Hey guys.... I have an 87 Fiero 2.5L. Switching over to the 3800SC. My question is do i use the 2.5 harness or the 2.8 harness with the 3800 harness. I ask this bc I'm losing this isuzu trans from my car and using a getrag 5 speed out of an 87 GT, which harness would be easier to use or would it make a difference. I would think bc the GT harness is already wired for the getrag to go with that one but I'm not exactly sure if it will really matter. Thanks

I'm no expert, but as far as I know all you need is the plug from the speedo sensor. Almost everything else gets replaced with the 3800 harness.

Ok great....thanks!

You also need to have the right automatic or manual harness i know i will struggle to find L67 5 speed manual harness off the shelf.

[This message has been edited by Australian (edited 11-15-2015).]

So then the GT harness with the getrag plugs and wiring would be the better choice to use then and splice that into the L67 harness?

quote Originally posted by Detainabull: Hey guys.... I have an 87 Fiero 2.5L. Switching over to the 3800SC. My question is do i use the 2.5 harness or the 2.8 harness with the 3800 harness. I ask this bc I'm losing this isuzu trans from my car and using a getrag 5 speed out of an 87 GT, which harness would be easier to use or would it make a difference. I would think bc the GT harness is already wired for the getrag to go with that one but I'm not exactly sure if it will really matter. Thanks

From the Fiero harness...
C500
C203
B/U light connector
Speedo connector
Pigtail from the Battery Junction Terminal

Everything else will be from the 3800 harness.

Your 2.5 harness will work fine for this.

[This message has been edited by olejoedad (edited 11-15-2015).]

If you intend to build your own harness it is a painstaking job. DarthFiero (Ryan) has been generous enough to share the wiring connections on his Sinister Performance website. Wire the connector pinouts as they are listed and everything should work out fine. If you wish to buy a pre-built plug and play swap harness Phil Dull (Injectech) seems to be the only reliable harness source right now

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

I'll definitely keep him in mind but I'd like to try this myself first. If I mess up I'll have to buy one anyways so I don't mind giving this a shot as I enjoy learning and doing new things.