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Foglights w DRL and Cargo light w reverse wiring mod help

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2020 Sierra 1500 SLT

After searching and reading through many threads without the specific answers I'm looking for, I'm hoping for some advice and information.


I'd like to have

1 )the fog-lights come on with the parking lights, so the fog-lights are on all the time (even staying on with high beams if possible)

2) the Cargo Lamps illuminate when the truck is in Reverse.


I'd like to know what plug/pin number to jump with the diode and what size diode/direction the diode goes (which way the stripe faces). Bonus points for photos (see below)


I found this photo in a 2014 - 2018 GMC thread. The thread said the brown to pink is the cargo-reverse light mod and the brown to brown was the parking lights-fog lights mod.


Are the plugs/wires/diode direction the same for the 2020?

Is the 1Amp D1 diode the right one for these mods?


I'd appreciate any help that can be provided. Please be sure to dumb it down for me and any other future searchers. I know I need all the help I can get!!


Thank you for your time,





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Disclaimer:  This is based off the upfitter manual schematics and technical data, It would be best to look up and confirm and verify this information before you make modifications!

To activate the Fog lights with the parking lights you can use a diode to jumper the relay controls:

fog lights relay controls is X5 (brown? connector) pin 10, BRN/WHT wire

Parking lights relay control is X5 (brown? connector) pin 22, BLU wire

both are ground triggers for relays so to activate fog lights with parking lights:

diode jumper Parking Lights Relay Control BCM X5, pin 10, BLU wire (GND signal) to Fog Lights Relay Control BCM X5, pin 22, BRN/WHT wire (GND signal), diode stripe goes towards Parking Lights, BLUE wire

refer to the upfitter manual, pages (these are from the 2020 sierra book, pages may vary some with other years or for the silverado manual)

7-255 for BCM connector X5 pinout

2-24 for fog lights control schematics

2-28 for parking lights schematics, as an example. the parking lights are actually on a number of different schematics. , 2-31, 2-32. 2-33 etc.


for cargo lights on with reverse lights,

backup lights relay control is X5 pin 26 BLU/BRN wire, note, this is a +12V relay control wire, not ground like usual. This relay is labeled the trailer backup lights relay in the schematic. according to the schematic, it is responsible for sending the reverse lights command to the tail light assemblies (for sierra LED tail lights, others may be different)

cargo lights (standing lamp relay control) is BCM X6 (pink) connector, pin 26, BRN/WHT and this also is a +12V signal.

so for cargo lights on with reverse lights

diode jumper backup lights relay control, BCM X5, pin 26 BLU/BRN  (+12V signal)  to cargo lights relay control BCM X6, pin 26, BRN/WHT (+12V signal), the diode strip goes towards the cargo lights, BRN/WHT wire

note that because of the two different circuits for the cargo lights, this should activate the cargo light on the back of the cab and the "hitch" light on the back of the tailgate, but will not turn on the interior bed lights.


7-256 BCM X6 pinout (cargo lights)

7-255 for BCM X5 pinout (reverse lights)

2-31, 2-32 for backup lights schematics

2-38 for cargo lights schematics


in both cases the only extra load we are adding to the source signal is a relay control, very low current draw. any standard diode will be fine.


If anyone sees any errors, please let me know!

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