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Putting in a temp gauge on a 72 cutlass 350 w A/C. Having some challenges locating an existing hole that can be used and cause no harm. It’s a Bosch temperature gauge with a fairly thick cable.
Any recommendations on any existing access ports in the firewall that can be used or if a new hole must be drilled and if so where?
I assume this is a mechanical gauge? That "cable" is the Bourdon tube that uses expanding fluid to operate the gauge. Your best bet is the accessory grommet that is outboard of the brake booster. This grommet has metal fingers that snap into the firewall. You will have to pop it out of the hole, run the sensor tube, slit the pre-molded cutout in the grommet, and reinstall it around the sensor tube.
On my 67, there is a grommet close to the passenger side of the engine on the center firewall to feed through. This way, the tube runs along the top side of the engine manifold to the port in front of the carb. I don't like the idea of the tube crossing from the fender well through thin air to the engine.
Last edited by oldcutlass; Oct 1, 2023 at 02:26 PM.
Unless the car came with power windows, power seats, a hood lock, or other power options, the hole / grommet shown in post 2 will likely not be there. There will simply be a dimple in the firewall where the hole needs to be drilled. If you zoom in on this pic of my 72 that was a factory 350 A/C car, you can see the 2 holes for the parking brake pedal studs, but there is no hole for the grommet in post 2. That said, I did drill a hole for that grommet on this car when I added all of its power options. Drilling that hole would be difficult to do without pulling the inner fender on the driver side unless you pull the parking brake and fuse box to drill the hole from the inside.
As an alternative, there is a large hole with a rubber grommet near the center of the firewall where the vacuum lines and wiring harness for the A/C system pass through the firewall. It is not the easiest area to access from inside the car, but if you are looking to avoid drilling a hole in your firewall, it is what I would use. You can see it circled in blue in the photo below.
