I'm installing my Holley 950 system and i had thought it would be easy finding a spot to cut the 2" hole in the firewall for the wiring harness to pass through. I was wrong. Does anybody have any suggestions? I want it to be on the passenger side of the vehicle. There isn't any room due to the heater core box.

I would imagine the length of cable/harness would determine the placement of pass-thru hole.

Most late model EFI vehicles have the harness through the area between the kick panel and the A-pillar.

Since 1st gen's didn't come with EFI, I would think any place close to the mid body mount-to-subframe around the upper toeboard area would be a good area. Like I said, depends on harness length and location of box.

My Fast harness was pretty long I cut the 2" hole right behind the drivers side head below the valve cover flange, the harness was long enough to mount the xfi box in the glove compartment. most of the sensor wires are hidden behind the distributor and cant see the huge two inch grommet behind the head. Worked out nice. There is one 3/8 inch grommet I snuck out below the bottom of the heater box, the wires for my msd box since that is mounted under the dash as well, there really is no room on the pass side if you run the stock heater box, unless you want to drop down onto the upper portion of the pass side floor kick/foot panel.

Rich

I ended up cutting 2 holes. I went through the upper most corner of the firewall on the passenger side, into the cowl area, then through the corner of the cowl areea down into the passenger area right above the heater box. Turned out pretty good and can't see it at all once the cowl panel is back on.

I'll be struggling with this soon too, but I'm gonna add a twist or 2.

Everything possible will go under the dash. Since I have a vacuum gauge, the map sensor will T in under the dash.
Rather than put in yet another coolant sensor, I'll tap that wire into the sensor lead on my autometer gauge, and recalibrate the coolant tables in the c950 to match with whatever reading it happens to get.

Then I'm gonna find some sort of twist lock connector, possibly a mil-spec connector, hack up the harness, and put the connector in the firewall, just to the drivers side of the distributor.

As mine is a TBI, and ALL it's wiring will come off the throttle body, I'm hoping to reduce the size of the bundle as much as possible, wrap it with factory nostick tape, and go back under the air filter, around the distributor to the connector, and make every wire vanish. They're gonna hafta look real hard to see it's anything but a 4 bbl carb.

Rather than put in yet another coolant sensor, I'll tap that wire into the sensor lead on my autometer gauge, and recalibrate the coolant tables in the c950 to match with whatever reading it happens to get.Might be an impedence mismatch, collection of 3 parallel resistances. Science project will tell.

Since I have a vacuum gauge, the map sensor will T in under the dash.


That's going to give you pretty bad lag on MAP changes and will probably make transient tuning kinda ugly. The line to the MAP sensor needs to be as small, short, and stiff as possible.

Good thread on it here:
http://www.thirdgen.org/techboard/diy-prom/210346-effects-length-map-sensor.html