1st of all i tried searching and could only fine one unresolved mention of onstar and the Hardware Hack. So i apolgize ahead of time.

In my setup i'm using the GMOS-04 Adapter by METRA to adapt my Bose/Onstar equipped 2006 Trailblazer to work with my newly purchased F90BT

The GMOS-04 harness has VSS, P.Brake, Reverse, Mute built right into the harness and in the instructions says to just attatch them to the radio harness wires.

i'm thinking i need the MUTE in order for my onstar to kill the radio when the button is pushed.

Is there another wire i can relocate/use in that 4th position on the NAV harness (maybe one of the 8 wires on the power harness for speakers that i'm not using because the GMOS-04 uses RCA Outs?? can i remove one without messing up the head unit/is it the same gauge/connector?)

What should i do with the wires on the harness? if i'm supposed to ground the parking brake and mute(or whatever wire i end up using)...i'm assuming i don't make the connection for the parking brake wire between the radio harness and GMOS-04?

I am having mine done tommorow meb and am in same boat. What I did to get around the mute wire moving is I looked in an old computer and found a similar plug and removed the wire from it and put it in the F90BT harness. Doing that you will keep the mute working in case you use onstar, so when you hit the button it mutes your radio for onstar.

And no you do not want to hook up the parking break wire from the harness to the GMOS-04. BTW you could have asked this at the trailvoy forum!

you can use any other connector on that plug that isn't needed for your application

Why don't you do a software bypass? No need to move the mute wire.

either do the software mod or use the power antenna wire (blue wire, same harness) to do the bypass, since the trailblazers dont have a power antenna.

not looking at the harness right now but why did i think the only other wire (besides RCA's) besides the mute wire on that harness was the blue remote amp turn on wire.....thought antenna wire was on the other harness.... they are both blue...maybe i'm wrong...

can anyone confirm which blue wire is on the NAV/RCA harness?

it seems the wires use different connector styles between the 2 harnesses too. so i dont think i can pull a wire off the other one.

yeh sorry, it is the amp turn on wire (blue/white)

i forgot a step... move the blue w/ white stripe wire over to the bypass spot, THEN in the AV settings menu turn Ant Control to power instead of radio (then the radio will power up that wire any time the system turns on)and then use the antenna wire as your new amp turn on wire

ok so here's what i did.

I did the standard hardware bypass (mute wire moved and grounded, p. brake wire grounded)

This DOES NOT disable my ONSTAR. when i push the onstar button it shuts off the radio and the GMOS-04 takes over.....

this would be annoying if i USED my ONSTAR. but i do not. the only reason i wanted it retained and usable is resale value years down the road.

i'm extremely happy with the system.

ok so here's what i did.

 

I did the standard hardware bypass (mute wire moved and grounded, p. brake wire grounded)

 

This DOES NOT disable my ONSTAR. when i push the onstar button it shuts off the radio and the GMOS-04 takes over.....

 

this would be annoying if i USED my ONSTAR. but i do not. the only reason i wanted it retained and usable is resale value years down the road.

 

 

i'm extremely happy with the system.

Moving the mute wire back to it's original location and doing the software bypass will fix the radio shutdown. Just FYI. I have onstar and I hit the button by accident one day, I didn't want to deal w/ the radio shutdown anymore.