Principles Of Operation

Upfitter Relay Box

Principles of Operation

NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

When the ignition key is in the ON position, the upfitter switch assembly receives voltage through the SJB fuse 42 (10A) which is distributed to the 4 circuit control switches. When a control switch is closed it supplies voltage to 1 of the 4 upfitter relays (solenoid side) in the upfitter relay box, closing that relay. Voltage is supplied to the switched side of the upfitter relay circuits from the Battery Junction Box (BJB) for relays No. 1 and No. 2; and from the SJB for relays No. 3 and No. 4. When the relay closes, voltage is supplied through the relay to the output circuits (and to the blunt cut ends) located under the LH side of the instrument panel. The output circuits (at the blunt cut ends) supply voltage to the installed accessories that have been connected to the upfitter relay box.