Drilling Hole for ECU

Ricks911s · 02-03-2009, 11:06 AM

Can someone show me a photo that shows where the ECU harness goes thru the firewall on an 81 SC or a similar car? I would like to drill a hole tonight for the pass-through for the wiring harness from an 81 SC engine (1976 body).

Thanks.

safe · safe's Garage

Without knowing for 100%, I think the harness is routed down behind the firewall, over the torsion bar tube and in the central tunnel.

Bill Verburg · Bill Verburg's Garage

Most of them go thru the firewall by the left rear shock

This is a 993 harness in a '76 C3 but yours would be similarly routed

Ricks911s · 02-03-2009, 12:18 PM

Thanks for your speedy responses guys. Since I'm using the brain/harness that came with the 81 engine I'm worreid about the length of the harness if I mount it any other place except for where it was stock, i.e. I think that the 81 SCs mounted the brain/ecu under the passenger seat. I think the 3.2s mount under the driver's seat. That's why I'm trying to get the right place down. What drill bit size did you use?

Thanks again.

felixcontour · 02-03-2009, 12:20 PM

Quote:

Originally Posted by Bill Verburg

Most of them go thru the firewall by the left rear shock

This is a 993 harness in a '76 C3 but yours would be similarly routed

Bill, I think the issue is that there is both a chassis wiring harness and a separate harness going to the ECU under the passenger seat. It seems to me that the ECU wiring would go through the firewall closer to the passenger side, based on what it has to hook up to (the O2 sensor, etc). I could be wrong.

A poster mentioned in a different thread that a hole would need to be drilled to run the lines to the ECU, which also seems to suggest that it is in a different location than the wiring harness that runs down the drivers side.

I'm no expert, so if I'm wrong feel free to pipe up!

Mark McClure · 02-03-2009, 02:29 PM

Hi,

Not sure if yours is the same but on my car the hole is in the rear passanger footwell. Left hande side of the car. It is a 50mm bung and there should be ties on the body to hold the wireing in place, comes up and into the engine compartment.

Hope that helps without any pictures.

Mark........

Ricks911s · 02-03-2009, 02:55 PM

Thanks. If any SC guys have a picture of where this hole is, I'd be much obliged. I wanna drill the hole tonight or whenever I can figure out with confidence where it is.

Cooper911SC · 02-03-2009, 05:16 PM

HI Rick,

I'll look at my '81 tomorrow in the daylight and find out the info you need...sorry I didn't see this post sooner...hold tight for the info. unless someone else chimes in.

Coop

felixcontour · 02-04-2009, 10:58 AM

Quote:

Originally Posted by kristan

Here is a pic of the hole for the DME harness.
The rope shows where the wire went.

Christian

Christian was nice enough to take a quick picture and put it on Rick911's other thread.

jcunning · 02-04-2009, 02:28 PM

Here is where I put mine. I think it is pretty close to where the real hole is located.

felixcontour · 02-04-2009, 02:51 PM

Sweet! Thanks Jeff! That's really helpful.

dezzmo · 02-04-2009, 02:59 PM

Quote:

Originally Posted by jcunning

Here is where I put mine. I think it is pretty close to where the real hole is located.

This is also where I ran the wiring harness in my 73 when I upgraded to a 3.2.

onboost · 02-04-2009, 04:12 PM

That's the proper location for the harness hole. Just as the factory placed it on the 3.2

Cooper911SC · 02-04-2009, 05:34 PM

Hi again Rick,

Sorry for the delay...got busy today.

On My '81 SC the Lambda Control is mounted under the passenger side seat in the stock location.

The harness runs along the outside edge of the center tunnel. Then up to the center of the firewall under/between the rear seats. There is a hole there which it passes through. This is essentially just above where the main harness comes out of the tunnel just beneath. Another way to describe it is that it passes through centered and just above the cover for the shift coupler.

Here are some pics.
Location under seat.

Harness running along edge of tunnel...sorry about fire extinguisher mount in the way...

Pass through hole for harness

Hope this helps you out. After the harness enters the engine bay it is routed along the rear of the firewall and over to the left side. The connector/mount for the O2 sensor is located just under the fuel filter and accumulator.

Take care, Coop

avt007 · avt007's Garage

Great pictures, very handy since I'm doing the 2.7 to 3.0 swap too. Jeff C, I noticed the fuel lines have been disconnected in your pictures. Were they hard to take apart? My rubber lines have been cut, and if the couplings come apart after 32 years, I'll just replace those sections.