Peterbilt 520 intake heater relay location

Have been working on a Peterbilt 520 refuse truck with the cummins L9 360 engine and have had a active code for engine intake air heater 1 circuit. I'm trying to diagnosis it but i am having trouble locating the possible location of the relay and/or fuse that may come in these trucks. Because from my knowledge peterbilt and other brands all put them in different locations. Would anyone know where this relay be located?