I used the one linked below. No cutting or splicing on the truck or opt7 side. , it is a 5 pin so you can use a bullet terminal on the white wire(reverse wire) of the opt7 light bar and plug right in to the 5 pin harness of the above curt adapter I speced below.
CURT 56584 Replacement Vehicle-Side Custom USCAR 5-Pin Trailer Wiring Harness
https://www.amazon.com/dp/B007EA6WQU/ref=cm_sw_r_em_apa_i_tBCMEbJW57VWF
I also posted below a not so great pic of the 4 pin opt7 plug connected to the 5 pin curt plug with reverse wire plugged in separately.
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