Ground Wire for Heater High Speed Relay

[ChomperDog]

Does anyone know where the ground wire for the heater's high fan speed relay terminates at? This is an 89' Suburban but trucks should be the same I would think. Tracing that ground up behind the dash behind the ductwork won't be fun. I'm hoping someone has already been there done that and can point me to the location of where this thing actually bolts to ground.

Thanks