I believe behind and close to where the heater box is secured to the firewall then down to the passenger kick panel area. There should be a mounting hole for the screw.
Hi Don. What wire is it that grounds to the center of the retainer bracket where the heater core lines/pipes go through the firewall? There is a screw at the center of those two pipes and a bit lower of that center. That is where I grounded/attached that wire. Just asking right or wrong I do not know. JJ