If the 05 is the same as my 2004 LM7 from an Avalanche, the harness from TAC to pedal is GM 15119525.

 

I was looking for the location of the harness under the dash, not the P/N. But thank you.

 

Sorry, misunderstood your question. So you found the harness with the 10 pin male connector at the TAC and can trace that wiring to the firewall but can't locate it on the other side?

 

That is correct. It does not seem to terminate under the dash at all. Keep in mind, this is a factory manual transmission truck. The harness goes through the firewall with the main harness, but I do not see anywhere it comes out under the dash.

 

That is odd. You should be looking for a 6-wire harness with a 10 pin male connector on the pedal side of the firewall. Can you pull the firewall grommet out to help find where it goes? I don't actually have an 04 Avalanche to describe where it should be under the dash. I bought my engine, pedal, and harnesses off craigslist to swap into my 69 Camaro and they were already pulled.

 

I see where the main harness comes in, and it's all taped obviously, but there's no way that tape is hiding a connector of that size. I pulled the footwell fuse block, thinking it could be taped behind it or something, but no. On automatic trucks, the harness runs through where the clutch master cylinder would be on manual trucks. So on a factory 4.8/manual transmission truck, I have no idea what they do with the TAC harness.