Has anybody swapped an ENTIRE LS1 harness in their thirdgen? Not just the engine harness, but the whole underhood harness as well, to include 4th gen Underhood Electrical Center (Fuse/relay center) and 4th gen cruise control?

The LS1 I picked up came with ALL underhood wiring including the fuse block and passthrough connector for igntion switch.

Beleive it or not, but the ignition switch connectors looked just like my thirdgen connectors, so I pulled up '90 schematics and '99 schematcis for ignition switches and they looked like they were just photocopied! All the Connectors and Pinouts are the same for ignition switches. The 4th Gen wire harness amazingly fits in the thirdgen. The passthrough connector is a little smaller, but features a bolt hole to secure it to the firewall, just add sealer.

The fuse/relay center will go were my battery used to be, and the cruise control will go were the old vacuum servo used to be (where mine was anyway). Heck, even the fan wiring fits my dual fans!

Has anybody else tried this? I'll post pics of what I'm talking about.

 

Fatal88 is the man to talk to. His car is a work of art, EVERYTHING under the hood is LS1, to include the sheet metal, the firewall and entire interior.

 

i did it that way.. are you positive about the column? i looked and it looked alot different as far as the plugs went.. including like the stereo controls, wipers, airbags, etc.. and what not before I swaped them over.. oh well after all the work im not puttin the 3rd gen one back in.. i also need the bags to work if i ever have to get the car safietied so the dash lights blink the correct way.. i even have the sensor mounted in the console and it all works awesome except the abs which i trashed.. i probably coulda made it work but who needs it.. just adds clutter.. capped the connector and plugged the light on the dash

i have used everything tho.. the only thing that doesnt work 100% is the delay wipers but im pretty sure i will be able to get the low and high and the chance of me being in the rain is unlikely.. i may plan to add a/c later so im not sure about that...

i have the stereo and theres a bit of wiring for the power antenna as there's has a built in relay and ours is under the dash

the next hurdle is the pop up hatch.. it has the same switch to pop it but it needs 12+ constant to a wire in the back for the light and pull down mechanism

the worst part is the lights.. about 20 wires to splice in the front and 20 in the back..

doors are straight forward only have to pull the one wire back for the door switch...

i used the 4th gen tank as well.. the 4th gen plastic lines with the fuel filter bolt right up to the 3rd gen lines.. kinda.. i had to splice in the evap line to the return line.. from the front end i made a -6an hose to a compression fittin on the fuel rail.. not many leaks

i mounted the computer on the pass side fender as it was the only place it fit.. i dont have any heater box so who knows where it will go if i get a/c... the engine lines come from the driver side and barely slip thru behind the rad..under there and out where i relocated the battery too, then around the frame rail to the plugs on the ecm.. it fits pretty good there and I didnt have to cut any lines and everything snaped in and the car started right up.. easiest ls1 wiring job in a third gen

if you have a camaro you will need a camaro harness.. and firebird to firebird..

are you using the dash and what else? i wouldnt wanna wire up the 4th gen harness to everything on the 3rd gen dash..

 

Yikes! I only used the underhood harness, not the whole vehicle harness! My swap has been done and 90% of components work. I've been to lazy to finish the rest. Items like the cruise control and wipers required alterations. I re-used my 3rdgen dash harness and spliced it into the 4thgen underhood harness.

 

im gonna have to look now to see if the 3rd gen turn signal/cruise stick thing is gonna work if you can make it work the other way it should work the way i need it too prolly end up breakin it like i did that ****ty plastic horn mounting thing in the column that i cant get out now

how/where did you mount the ecm? i was thinkin of maybe moving it onto the driver side and extending a couple of the connectors so i can get the a/c box in

 

any luck with all of this? i'm putting a ls1 in my 91 convertible and i'd like to keep most if not all of my factory thirdgen interior/guages. i tried calling a few places like speartech and $1,200+ seemed a bit much to keep my factory guages.

anyone know how difficult it is to tie your factory thirdgen dash harness section into a 4thgen ls1 engine harness and ecm?