Manuals through 2025 now available!

Our trusted friends have launched a new website named LEMON, which has newer manuals. It also contains all the CHARM manuals.

LEMON is the spiritual successor to CHARM, I recommend you try it!

Link: lemon-manuals.la or lemon-manuals.org.ua

(Some people have issue connecting. LEMON is investigating. For now, use Firefox or change your DNS server)

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Principles of Operation

Upfitter Relay Box

Principles of Operation

When the ignition is in run or accessory, the upfitter switch assembly receives voltage from the Body Control Module (BCM). The upfitter switches control the 4 upfitter relays in the upfitter relay box. When the relay is energized, voltage is supplied to the customer installed accessories.