What used to be here?

[strutaeng]

Yeah, looks like a grommet for wiring. The wiring from the fuseblock to the cab I believe has something that looks similar to this.

 

[the 18th letter]

Looks like part of the tailight harness.

 

[PG01]

Looks like part of the tailight harness. View attachment 411078

Bingo. We gots a winner…..

 

[TollKeeper]

I would imagine its the same wiring harness for the Tahoe and Suburban.. They just bundle up the extra wiring for the shorter length needed, and zip tie it down.

 

[Hoesgottaeat2]

...Possibly where the trailer harness was zip tied until it was wired in...

Looks like part of the tailight harness... View attachment 411078

I'd say between @Eman85 & @the 18th letter, you guys nailed it. Thanks