Does anyone know what goes in this spot on the firewall?
It’s part of the NOX system. I believe it was a 1972 California only setup. Wires go to a sensor in the middle of the speedo cable (right below the master cylinder), the ballast resistor, and to the OSAC valve between the carb and vacuum advance. It measures ambient temp and takes info about your speed to determine whether or not to block your vacuum advance. Mine had long been out of commission so I removed it and put a 1” round rubber seal which fit the hole perfectly. It’s also straightforward to remove the wiring sub-harness for it. You can also change to a one-piece speedo cable once it’s gone.
It’s part of the NOX system. I believe it was a 1972 California only setup. Wires go to a sensor in the middle of the speedo cable (right below the master cylinder), the ballast resistor, and to the OSAC valve between the carb and vacuum advance. It measures ambient temp and takes info about your speed to determine whether or not to block your vacuum advance. Mine had long been out of commission so I removed it and put a 1” round rubber seal which fit the hole perfectly. It’s also straightforward to remove the wiring sub-harness for it. You can also change to a one-piece speedo cable once it’s gone.