Hi, does the firewall insulation go on before the heater box or after? Been a long time since I took apart, don't remember and can't find any diagram showing it. Thanks

 

If you are referring to the interior side firewall pad then THE PAD goes on first and the interior heater(or AC/heater) box goes on OVER the pad. No need for any gaskets, silicone, etc.....the pad surface will seal up against the lip of the box.