GMT800 Cab Swap: 2002 → 2003 1500 Ext Cab, Rust Control & Questions

[SilveradoPhil]

Starting a thread about moving the complete 2003 dash and HVAC/heater system into a rust‑free 2002 GMT800 cab. I'm swapping everything over — dash, harness, HVAC box, blower, and controls — and want to know what differences to expect between the 02 and 03 setups, wiring, and mounting points. Any advice from people who've done this swap is appreciated. More questions forthcoming. Thank You

 

[stutaeng]

I've never done a complete wiring swap, just know some of the basic differences between the 99-02 vs 03+.

I recommend you download all of the wiring diagrams from AllData or something similar. Study the diagrams and find any differences. Maybe create a list to check off as you are swapping away.

Good luck and interested in any updates.

 

[SilveradoPhil]

I've never done a complete wiring swap, just know some of the basic differences between the 99-02 vs 03+.

I recommend you download all of the wiring diagrams from AllData or something similar. Study the diagrams and find any differences. Maybe create a list to check off as you are swapping away.

Good luck and interested in any updates.

Thanks, I need it. I have done a complete dash an HAVC/Heater assembly. along with steering column and door wiring, not sure if i have to do the dome light too. Had I known that there was a big change from 02 to 03 I probly wouldn't have done it. It is a time-consuming job for sure

 

[stutaeng]

Thanks, I need it. I have done a complete dash an HAVC/Heater assembly. along with steering column and door wiring, not sure if i have to do the dome light too. Had I known that there was a big change from 02 to 03 I probly wouldn't have done it. It is a time-consuming job for sure

Yeah, it was a big change in those years.

When I did my 99 Silverado 5.3 swap, the 5.3 came with wiring harness and ECU from an 04 Yukon XL. I too didn't know then that there was a change in the system. A fellow on performancetrucks.net instructed me to go source a 99-02 wiring harness and an ECU, after me getting stuck on the O2 being completely different on the donor wiring vs my Silverado.

BTW, are you also changing engine wiring harness and ECU? Doesn't that have to match the newer wiring harness?

 

[AuroraGirl]

Yeah, it was a big change in those years.

When I did my 99 Silverado 5.3 swap, the 5.3 came with wiring harness and ECU from an 04 Yukon XL. I too didn't know then that there was a change in the system. A fellow on performancetrucks.net instructed me to go source a 99-02 wiring harness and an ECU, after me getting stuck on the O2 being completely different on the donor wiring vs my Silverado.

BTW, are you also changing engine wiring harness and ECU? Doesn't that have to match the newer wiring harness?

03-04 or so should have different oxygen sensors from 05+ and different cat converters (half ton I think)