Just a little follow up explanation of how my install came out with accompanied pics so you guys who are curious can see how i did it as there are some things different than others. Attached is a pic with colored arrows and below is the description of what they are; Red arrow is a fourth gen stock LS1 fuse/relay box year unknown but they are all the same from what I gather. - This is my main power source and feeds the entire car. I used everything from an LS1 for the engine. Starter cables and all. Fourth gens come with two of these boxes side by side and one is pretty much for the engine and the other is for the chassis. I decided to emulate that by using my stock third gen fuse box as my chassis circuits seeing as they all worked fine and add in only the engine box from the fourth gen harness to supply the engine and fuel system. Note my car was a factory carb so this made even more sense as I had to add fuel circuits too. The best part is all the wires are of factory quality and the colors match the PCM wiring so it made connecting them easier ( there is some overlap on colors for some reason so be careful ). I ran one 10 awg+ wire from this box to feed my stock fuse box under dash box. I used an LS1 fuel tank as well with stock pump but wired with the Hotwire mod so it gets direct power via the fuse box and only triggered by not routed through the PCM. Green arrow is the trunk line that takes all the wiring from the added fuse box to under the dash where I mounted the PCM. It goes through a hole under the heater box and if you look carefully there is a heat shield for it beside the header as a safe guard as it is close to the headers and I wanted to avoid problems. Yellow arrow is my ground block. Every single factory ground from the engine harness, PCM, or my factory third gen fuse block goes here. Its a 3/8" stainless bolt and all my connections are soldered to good quality eyes. Any that did not reach I extended thinking that this way if I have any troubles finding the "bad ground" its dead easy. Ground problems are almost ALWAYS the source of electrical gremlins in automobiles due to the floating ground system they use. I also added many new grounds to and from the engine/chassis/trans/battery etc they are all over the place so I dont have to rely on the fasteners to carry the ground. Cant have too many grounds wire doesn't weigh much and its an easy way to avoid mystery problems later on. Trust me you will forget where all those wires go after a year or two. Blue arrow is what I did to vent the steam tube from the heads. I bypassed it from the TB altogether and tigged on a small nipple to this stainless tubing I had. Its very thin wall stuff ( sheet metal ) so it weighs as little or less than the hose. I cant recall the alloy but its hard stainless so tough as snot. I have a bunch of this too if any of y'all want one let me know. The second pic is a close up view of the stock LS1 fuse/relay box opened with the cover beside so you can see whats in there and how slick it is. I have one spare circuit which is the slot with no fuse in it and two spare relays in there in case i have troubles I am prepared. The BIG fuses are for 1. the LS1 fuse box power supply 2. the power feed for the stock third gen fuse box 3. is for my amplifier/sub box which has an 8awg cable running to the rear of the hatch. All nice and neat inside one box thats OEM rated and easy to access. Plus I have eliminated the factory fuseable links by replacing them with these replaceable easy access ones. Nothing in my car is not fused right there so its a very safe set up. The one marked "etc" with a 20 amp fuse is actually my fuel pump fuse for whatever reason it was in the second LS1 fuse block even though the relay was in this one so I moved it over. The 25 amp in the top right corner is for my cooling fans and for these I used my stock third gen relay. Oh yeah Its not two boxes in the pic its just the lid off this one laying beside so you can see the labels as the other fuses do correspond to what the lid says. I have other threads already posted up in days gone by of all the other mods I have done but if you have any questions ask away

That's so clean! Mad props to your clean, factory looking setup!!
Just a quick question, I know this thread is old as balls but, how did you connect your engine harness to the fusebox? or was it already connected like that??

Hmm I thought I explained that above but let me try and clarify. Right beside the battery there is my LS1 fuse/relay box which I added this is from a 99LS1 donor car. The +bat cable hooks up to this just as it would in a fourth gen and that fuse/relay box powers my engine, PCM, fuel, cooling fans, A/C etc. Everything to do with the LS1 engine gets its power from that box.

I still use the stock third gen fuse box thats under the dash below the brake booster to run the chassis circuits like headlights, power windows, interior lights etc.

Yea I understand what it does, I ment to ask you exactly how is it integrated to your harness? Did you have to cut and splice every wire into the fuse box? Or are there quick disconnects or something? Just trying to get an Idea of how hard it would be to do this...

I actually kind of have the same question... How does the fuse box physically connect to the rest of the engine harness in a stock 4th gen f-body setup? Does it plug into the harness or is it hard wired?

I have a truck harness for my swap, but I don't want the massive truck junction/fuse box...

Ahh I see I can explain. With LS1 engine harnesses there are 5 plugs that come off the back of the engine harness plus the two PCM plugs that feed the entire operation. My engine is a 99 so I was thinking was if I bought the same year/model correct fuse boxes with the wiring and relays intact with the female plugs still hooked up all I would have to do was literally plug them in to my engine and just power up the new box and I'd be rockin. Sounded sensible and simple enough so thats initially what I did. To get the harness I posted a "wanted 99 chassis harness" post up in the parts wanted section over at Ls1tech and got a response within hours and had what i wanted underway from a board sponsor over there. After reading all the titles for the different circuits on the two boxes I realized I only needed the one as the other was primarily for chassis circuits.

So after studying the two boxes I realized I could easily eliminate one box ( chassis one ) and instead of using the 5 plugs to mate to the engine harness I would just solder the wires needed instead to both save space and clutter. The wire colors did match up nicely as well so it was pretty easy to do it this way. Then all I had to do was add +bat to the fuse box and run one +bat circuit over to my stock third gen box under the booster which i did and that took care of the rest of the car I just left all the other stock circuits intact they are just along for the ride now but do nothing.

Wiring is hard to explain up front and you'll never plan it all out in your head ahead of time. Just label everything and get everything plugged in and laid out in front of you and it will start to make a lot more sense.

X10000000...

It'll scare you at first... then become less and less intimidating once you start ditching things that you dont need, and cleaning things up. It'll make perfect sense once your done. Not only that, but you'll be able to trouble shoot future elec. problems because you'll know that harness inside and out.

Ide like to consolidate my fuse blocks... I just left both boxes in place. But now that I want to stick my air filter further over by the fender, Ide like to make one box, and re-mount it.

J.

It wasnt hard to do at all. The only thing about that set up I found kind of dumb from the factory was the relay for fuel was in the box I used but the fuse for it was in the other one so I had to add a fuse in this box to eliminate to other one and literally that was IT no other rework was nec. As for the five plugs because there were so many emissions related ones and other circuits that I wasn't using/needing and I wanted to run the PCM in the stock under dash location the five harness plugs took up waaaaaaay to much space to clear under the HVAC box as it is pretty tight under there. I do recall though on one of those five plugs I was only using one wire and I think two wires on another so for 3 connections I was wrestling with two 1" x 1" or perhaps bigger plugs so I thought as nice as it would be to have the ability to literally unplug the engine from my harness come time for removal I just couldnt fit everything all in neatly where I wanted. So come time to pull it out I just have to unplug the entire harness at all the sensors and snake it all out of the way which will take all of ten minutes so I didnt care. I think the drop in/out harness plugs are designed more for ease of manufacture rather than ease of service anyways.

I'm not certain if all the truck sensors are compatible with f-body PCM's and they all used drive by wire throttle bodys. Also depending on your engines year you need to determine what reluctor wheel count your engine/PCM operates on and you'll need to use a harness and PCM to suit that respectively. Either that or completely swap over to an LS1 f-body 24tooth reluctor and sensors/harness etc. These are the main reasons I comment in the sticky that for the "first swap" its so much easier to start with an F-body LS1 as the accessories all fit nicely and the harness is clean and easy( relative easy ) to swap in cleanly plus theres lots of support from guys here and over at Tech on how to do exactly that. Sheldon made a nice harness up using a hybrid LS truck/cavalier fuse box but IIRC he has an underhood mounted PCM which was something I definitely didnt want.

Awesome That's what I needed to know. Thanks for your help!!!!

No problem ask away if you need any more help or if any other swappers get into this thread and want to bring it back from the dead to further discuss ideas post away I'll do what I can for you as will others as well. Good luck

P.S. TT84Z5SPD I just edited and added a few clarifying elements to the posts above so have a re-read it should be clearer now

Did you have to do anything special on the heater box for clearance? If so can you get some close-ups

No I didnt mod the HVAC box at all to clear the wiring running underneath but it is VERY tight there and the wire looms are compressed by the HVAC box sitting on top of them so I wrapped them very well with harness tape, that black flexi conduit stuff, and used a good grommet on the firewall. I have no pics nr could I get any really its so tight under there I couldnt get a pic of anything anyways but check this link out below ( which is also in the main wiring section of the sticky now

http://www.thirdgen.org/techboard/lt...ight=pcm+under (LS1 PCM mounting under dash)

I went with a 6.0L cause it was cheap ($550 for the longblock). Granted, the total is getting up near 2 grand now with having to buy f-body accessories and other related stuff for the conversion from truck to car... Still less than a complete LS1/4L60E dropout, though.

I have a '99 Corvette PCM that I will be getting reflashed to a truck OS. My motor is an '01 with cable throttle (in the earlier years of the GENIII vortec I think DBW was only used on models with TCS).

As far as wiring goes, I think I am fairly competent. For that matter, I actually kind of like it. I just want to get away with it without spending very much money at all . And for now, I am not overly concerned with performance or appearance. I will focus (heavily) on all that once I get a steady income.

Thanks for all your guys' help. Now all I need to do is find a 4th gen fuse box for $30 or less. It's amazing how rare LS1 4th gens seem to be around here on the street and in junkyards. Thanks again!