So originally I took an unconventional route with my Terminator X harness routing to just get it done faster and ran it through the passenger side fender as pictured. Its not quite long enough to do that and have the ECM mounted anywhere I'd want it. Plus it gets in the way of the AC box as well now that I am putting the AC back in it.

I remember people taking the harness and running it through the AC vacuum and wiring harness grommet spot but it seems too small. I can get the biggest connector in but there's no room to then push it down and start pulling the harness through because the AC box is too close to the hole. I really don't want to have to pull the dash again... where did yall run the harness into the passenger compartment?

 

Above the PS frame rail on the firewall you can bore a 2" hole right on the pleat. Clears the inside AC box and is away from the exhaust

I recently built a holley harness, but used a flying lead to go the stock routing. It's 15' long

 

I have a thread on this exact topic that I recently started. Here is a link to the thread:

Where to mount my Holley Dominator in my 1987 IROC?

 

I'm assuming that you have the Terminator X mounted under the passenger side of the dash near where the OEM ECM was mounted.

 

Blown_WS6, I just realized that you've got a Firebird and the dash may be different than my IROC.

Where would you like to mount your Terminator X? I'd like to mount my Dominator under the passenger seat if the harness were long enough. I've got my Foxbody, Mustang coupe's Dominator (see signature below) mounted under the passenger seat. I had to cut a hole in the center of the firewall for the "as supplied" Holley harness to pass through.


I wanted to use the Ford factory oval hole that you can see on the passenger side of the firewall. The Holley wire harness was just a little too short to use that oval hole so I had to cut another hole right in the middle of the firewall.



The new hole looks like the factory did it!

 

if you drill a new hole through the firewall near the driver side valve cover, you can route the harness over to the passenger area behind the dash. it will reach. in the picture below, the hole is slightly below and to the left of where the wiper motor goes. the factory terminator X harness can be tucked up below / behind the HVAC box to where the factory ECU is located. you can mount the terminator X ECU to the factory ECU bracket. worked pretty good in my case but i had the interior gutted - including having the dash out.