harness routing
 

anybody used an OEM harness and routed it nicely in our trucks.
im looking to see where the replacement fusebox and the pcm has been mounted so i can get some ideas. im not really wanting to lengthen so many wires just to relocate the pcm but i wont mind lengthening the fuse box wires
pics would be awesome. thanks guys

Re: harness routing
 

It's not done as I will clean it up some and put it in some loom but I put the fuse block on the driver fender and ECM is behind the driver head light.

Re: harness routing
 

Using a van-based harness (its longer) I've had the ECM stuff mounted on the fenderwell (behind driver headlight), and then moved it into the cab under the glovebox.

Re: harness routing
 

I'm adding to the length of almost every wire in order to put my PCM under the driver side seat. My fuse and relay panel is mounted on the radiator support under my windshield washer container. The TAC is mounted to firewall under the booster/master cylinder. It's wearing me out making everything longer but in the end I think the harness will be kind of hidden. Michael I still have gotten your email, check your PMs

Re: harness routing
 

I always use truck harnesses. I mount the PCM under the driver side front fender. There's pics of them in my build threads. This is my Blazer, but its kind of hard to see the harness in pics.

Re: harness routing
 

Like others, I move the battery to the driver's side and put the pcm against the core support under the battery. The important thing is to not secure your wiring bundle tightly until you get the pcm where you want it to go. The battery on the D/S just works better (IMO) with the truck harness and gives more alternatives to the air cleaner/intake piping on the other side. HTH

Re: harness routing
 

michael Bustamante, here are some pics of mine. I hope this helps. This was a stock truck harness I modified to work with lq9/TH400 set up. My harness was kind of rat nestish, but it worked well. I didn't remove any wires from that harness. It worked so well that I sold the truck b4 I could finish it. I like to ensure everything works b4 I sign the deal and lock things down permanently. good luck.

Ls1Nova71, we gotta see more pics of the blazer. I been waiting to see it. I know its something special.

Re: harness routing
 

thanks guys thats exactly what i needed. one quesrtion though. did you guys have to lengthen the pink n oranges wires and the other wires to mount the fuse box to the driver fender?
I think my pcm is going to go under the battery tray once i move it to the driver side

Re: harness routing
 

sangel: did you relocate your battery?

Re: harness routing
 

I did not lengthen any wires on the engine harness.

Nope, it is in the stock location. I did make my own battery and battery-Alt cables.

Re: harness routing
 

yup i think thats gonna work for me. thanks bud

Re: harness routing
 

I just finished my ls swap in the 1968 suburban. If I was to do it again I would mount the pcm to the core support on the drivers side using the express van mount. The pcm will not fit under the battery tray on the drivers side it will fit on an angle beside the battery using a aux tray but it takes alot of time to just make it fit. I would use express van cables for a factory look keeping the battery on passengers side .

Air intake I would route to drivers side using a custom intake tube.

I would never use another rad with outlet and inlet on the same side again. its just stupid. My hot rad hose runs along my cold air intake that goes towards the passages side. The idea of a cold air intake is totally wasted with the tube running along the hot rad hose.

Re: harness routing
 

Great thanks for the info.... Im. Still open for ideas...

Re: harness routing
 

I made my own ECM mount so I could put it where I wanted and how I wanted it but it would for sure have been buried if I relocated the battery to the driver side.

My experience comes from the offroad racing world where running a dual pass (inlet and outlet on the same side) radiator is very common with LS based motors. It keeps the hose shorter and routing easier in a tight package. As for heat from the radiator hose affecting the intake air temp I would bet the air ingested from an under hood open filter and or the aluminum tubing if that's what's being used would be worse than the radiator hose heating it up. It would be and interesting experiment to test since a scanner will read I take air temp.

Besides doesn't the factory style hose run under the stock intake tube?
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Re: harness routing
 

I just looked at your thread and your Suburban is awesome.
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Re: harness routing
 

I finangled my ecm in behind the glovebox under the dash...never ever again will I do that...my next one is going under or behind the seat..I really didn't like the thought of it being under the hood but thats just me..I used a psi harness and if I had of thought about it I could have had them add length to it ..

Re: harness routing
 

how much extra length did you have to add to the harness to move it inside the cab? this is the ideal location for my swap but not looking forward to all those wires and soldering and heat shrinking everything. it will be done as right as i can do it but i am not looking forward to it.

behind the glove box i mean.

Re: harness routing
 

I used a psi harnesss not the stock one..it was plenty long enough to go thru the firewall and behind the glovebox..it wasnt long enough to go under the seat though...I was planning on using my stock harness but they cut it half in to when they pulled it.then they put the shield back over it and i didnt know it until I started working on it..with all the air conditioner ducting and stuff behind the dash is what made it so difficult

Re: harness routing
 

I would have preferred to use an aftermarket harness but this is my son's truck and he is responsible for 1/2 the expense so he's learning how and where to save when he can.
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Re: harness routing
 

A guy I work with is doing his own harness and he told me that he's got about 30 some odd hours in it..between research and work..now he's starting over and doing another one..says he learned what all he would change on the next one..to me its much easier to buy than build..I hate electrical...but that's great your got your son taking on responsibility on your build sangell

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We did not modify the harness we had it done but it was about 1/4 the cost of a new one and done by a guy I trust. Thank you but really this is his truck so if he doesn't put in time and money it wouldn't happen.

Re: harness routing
 

I didn't add any length, just moved the harness. Mine was a custom harness but its based off the van layout and wiring lengths.

Re: harness routing
 

Originally, I wanted to use the massive hole in my firewall to run the harness to the area above the HVAC box like the original 85 ECM box was.

However, after realizing that the PCM was bigger than the space (05 and up PCM would be a better fit there) and I would have to extend most of the wires, I decided against that and came up with a new plan.

The new plan is to leave most of the stuff right where it was in the 2003 Tahoe; giving it a more factory look, rather than custom. Here's the basics I did. Your year might be different.

1. Since the 03 Air Cleaner was on the passenger side, I mounted it to the original 85 battery tray.
2. Then I moved to battery to the drivers side using a Diesel battery tray i got in the Junkyard. This also kept the 03 battery cables in place which was good, since the 85 didn't come with any.
3. The 03 fuse box will be reused and placed right next to the battery on the fender well. Again, because that's where is was in the Tahoe. It did necessitate moving the windshield washer jar.
4. For a W/W jar, I used a 2000-2005 Buick Le Sabre jar and mounted it under the original 85 passenger battery tray. It has a big body at the bottom and long neck that sneaks up between the 03 Air cleaner and the core support. (not pictured) Looks so factory.
5. The Tahoe PCM was originally mounted down low on the drivers side. So I built some brackets and used the original hangar to mount it in that same area to the Diesel battery tray. No extra wires were needed. If I would have gone to the core support, I would have had to extend wires. So that was out.
6. Why did I use the big 2003 factory fuse box? It always bothered me that the main power wires used fuse-able links. So, during the re-wiring process, I moved a lot of circuits to this box. I now have the two main power wires that go to the ignition and 85 fuse box each on one of the massive 60 amp fuses and relays. Also utilized the starter relay to eliminate full power going through the ignition switch; which can cause them to fail. Also used the fuel pump relay to keep things clean and tidy.

This has worked out well and during the mock up stage, the 5.3 turned on, pumped fuel and started just like it did in the 03 Tahoe.

Future plans will be to run the headlights, parking lights and fogs lights through this fuse box as well.

It did take a LONG time to wire it up but I am weird and love wiring. :crazy: I took the challenge and spent a long cold winter in the garage soldering each wire, one-by-one.

It was fun because my 13yo daughter was with me and she learned a lot. Still talks about how she found some circuits that I couldn't. :tms: This will be her first car, so I want her invested in it.

The hardest part was doing it blind, without the factory 03 wiring diagram. I used most of the info from Brendon at LT1swap.com, google searches, AllData stuff from my local mechanic and sometimes just running continuity tests on each wire in the box!

All in all, I don't advise it unless you enjoy giving yourself headaches. :hh:

Here's some pics during the mock up stage. hope this helps.

Re: harness routing
 

wgesnerjr. great write up!

Re: harness routing
 

I used the truck harness that came with my 5.3 LY5. I took it apart and shorten to fit my truck mounted ECM & TCM inside the firewall by the original A/C box. You can see the harness going through the fire wall to the added on extra small fuse box i don't like to see wires when i open the hood.