Hot Rod Harness Routing

[Mastertech5]

I've been wondering how other builders run their harnesses from engine compartment to the interior. Do you guys cut the tunnel to accommodate the harness and seal it up somehow (silicone)? But then what if you have to pull the tunnel for clutch replacement or other repair. My LS3 fuse block and computer connectors are hardwired in and meant to be in the engine compartment on a production vehicle, not really enough room on the Hot Rod.Those sections of the harness are long enough to reach the interior where I prefer them to be. Grommets are out of the question unless they would be at the very edge of the tunnel in a slot cut and the grommet being cut also. Pictures and advise welcome.

[edwardb]

Truck here, but firewall forward the same as a Hot Rod. So some similarities. I have the main LS harness going through a notch on the RH side of the firewall. I have the LS fuse panel, PCM, etc. mounted behind the dash as shown. The harnesses from the cockpit to the back (main power, rear harness, transmission controller, etc.) I gathered and go through a notch at the top LH corner of the tunnel cover. Don't have a good picture of the final result. But just what went through there. The tunnel is removable, although (obviously) hope I never have to. I basically took the supplied RF harness completely apart and reconfigured to make everything is direct and space-saving as possible. I'm positive not the only way to do all that. But worked for me.

[33fromSD]

I drilled through the firewall and used rubber grommets.

20201201_080728.jpg

Jim

[FF33rod]

I followed the manual (essentially what edwardb shows in his second pic), cut holes in the forward part of the transmission tunnel cover, slotted the front part of them for the various harnesses to pass through - from what I recall their were already large grommets on the RF wiring harness. From the manual:

wire.jpg

Steve

[narly1]

Seals-it firewall grommets get my vote.

https://sealsit.com/tech-videos/

Earl

[RoadRacer]

I notched into the top edge of the transmission cover, and added a grommet there. that way you can remove the cover and leave the wires in place

[Mastertech5]

I like the way EdwardB ran his LS3 harness through the firewall on the passenger side. He only had 1 large conduit. I have 2 smaller ones, ECM and fuse box. I don't know if he put both into 1 or only had 1 for his setup. His ECM is much larger than mine. It looks like the older big aluminum finned one from about 15 years ago. Mine is much more compact. The Ron Francis harness does have grommets on it. There are 3, front harness, rear harness and the power from starter/alternator harness. I should be able to run those through the firewall without to much trouble. Time will tell. Thanks to all for your opinions and advise. Hope I can reciprocate at some point. Where would we be without this forum?

[edwardb]

I like the way EdwardB ran his LS3 harness through the firewall on the passenger side. He only had 1 large conduit. I have 2 smaller ones, ECM and fuse box. I don't know if he put both into 1 or only had 1 for his setup. His ECM is much larger than mine. It looks like the older big aluminum finned one from about 15 years ago. Mine is much more compact. The Ron Francis harness does have grommets on it. There are 3, front harness, rear harness and the power from starter/alternator harness. I should be able to run those through the firewall without to much trouble. Time will tell. Thanks to all for your opinions and advise. Hope I can reciprocate at some point. Where would we be without this forum?

Interesting. My LS3 and control pack were brand new from Chevrolet Performance two years ago. Maybe different engines have different ECM's and fuse boxes. Or they shipped me some really old stock. Oh well. Worked with what they sent me. The large conduit does split. But I moved it to where the split is inside the firewall. Made for a neater and cleaner install. I have the front harness going through the lower firewall and routed to the front inside the lower chassis rail. I found that to be more direct and neater than on the upper chassis rail. Didn't show that in my first post. I have the main power going through the firewall on a Blue Seas Systems ‎2204 3/8" terminal feed through. Starter and alternator attach on the firewall side. Main battery power and feed to the RF panel on the inside. Lots of ways to slay these things.

[Mastertech5]

EdwardB,
I'll figure it out. I like things to be neat like you. I didn't really want to run anything through a hole in the tunnel if I didn't have to. My LS3 harness splits those 2 conduits near the back of the engine. Maybe I'll get some bigger conduit and take the 2 off and run them together to the inside and then split them likes yours.
I read 9 pages of your build and am very impressed with your process and explanations. Thanks for your help!
One more thing, did you run your B+ cable through the tunnel and then to the buss bar? I was thinking of running it through there and straight to the starter.

IMG_20221020_140827_hdr.jpg

Here's a picture of the ECM. It measures about 4 1/4" x 6 1 /2 " not including the mounting ears. After looking at your picture again they do look the same. When I saw it the first time I assumed it was one of those old 8x10 ones from way back that used to split open in the winter if they were wet and then froze.

Bruce

[edwardb]

EdwardB,
I'll figure it out. I like things to be neat like you. I didn't really want to run anything through a hole in the tunnel if I didn't have to. My LS3 harness splits those 2 conduits near the back of the engine. Maybe I'll get some bigger conduit and take the 2 off and run them together to the inside and then split them likes yours.
I read 9 pages of your build and am very impressed with your process and explanations. Thanks for your help!
One more thing, did you run your B+ cable through the tunnel and then to the buss bar? I was thinking of running it through there and straight to the starter.

IMG_20221020_140827_hdr.jpg

Here's a picture of the ECM. It measures about 4 1/4" x 6 1 /2 " not including the mounting ears. After looking at your picture again they do look the same. When I saw it the first time I assumed it was one of those old 8x10 ones from way back that used to split open in the winter if they were wet and then froze.

Bruce

I ran the battery positive cable (#2 gauge from West Marine, good stuff) through the tunnel (upper corner of the driveshaft cover), above the transmission, and over to the mentioned 3/8" terminal feed through. On the cockpit side, there's a cable up to the bus bar where all the power inside the cab is distributed. On the firewall side, a short cable goes to the starter. Another to the alternator through a mega fuse. You can see the power cable and some of the routing in the middle picture in post #2 above. It's the one with the nylon mesh (as opposed to regular convolute) and you can see where it goes over to the feed through. My ECM looks exactly like the one you pictured.