The mirror can be wired to constant power because the display and auto dimming feature may be turned off, but it could drain the battery if left on for a long time. My car already shows ambient temp. Yes, it is a matter of placing the temperature probe inside the vehicle instead of outside. The probe should be routed underneath the dash along with the power cable. It may be mounted under the dash away from any heat sources.
Most vehicles have many wires already passing through the firewall.
Ideally it is best to locate a rubber grommet that passes such wires through, remove it, pass the temperature probe through, and replace it. Once the wires have been pulled through, they need to be spliced together. Route the probe around the drivers side door, under the quarter panel and into the engine compartment, or 2. Hear what other people are saying about our mirror products. Please mail your comments for now.