What they don't tell you is the new head unit even with the GMOS interface will not act like the old one. Meaning, more or less the sub will get treated as a door speaker. Your doors and tweeters will get bass they shouldn't be getting and distort easily. You'd have to add crossovers to separate everything unless I'm missing something. I'm having an issue right now after installing a new head unit. I'm thinking about going back to the stock one until I can afford an amp, new subs and wire to rewire everything. My aftermarket unit has crossovers built in. When I use them it takes away from the sub. When I turn them off everything gets distorted at higher volumes when it didn't with the factory unit. It's been annoying to say the least!

 

I always thought using the factory harness and the chimes feature would have been the same as the OEM head unit. Both my HHR’s have the pioneer seven speaker system, I’m gonna stay with that and not mess with it.

 

I thought the same as you and that doesn't seem to be the case unless I'm missing something. I can't think of any other reason the system would behave this way. I was actually looking through auxiliary Bluetooth devices last night. That's one of the reasons I installed the new unit. I had it laying around not being used and I wanted Bluetooth. I figured it would also allow me to have more control over the sound and it seems like I have less control now.

 

I seemed to have figured out the issue. Well, atleast most of it. I started tearing everything apart and noticed a tiny little bluish colored screw on the GMOS interface. It's a volume control! I turned it all the way to the right then about a quarter turn left and everything sounds much better now. Using the crossover on the head still does pull bass from the subs but it sounds fine without crossing them over now. The head unit must have been clipping instead of the speakers distorting like I had thought.

 

I read the gmos owner manual last night and was going to mention it, but since my turban isn't working I thought you already RTFM'd. Crutchfiels.com has the manuals online.

The HU is a pre-amp, no sub-woofer output. The amp does the cross over stuff.

 

I got my interface pre owned so I didn't get a manual with it. It really didn't seem like something that really needed much direction. Match the colors and plug it in. I'm pretty new to this whole car audio thing and just figured it was worth it to share my learning experience with others on the same path as myself.

 

Matching the coloured wires is easy but some kits don’t have the colours matched to the OEM harness .
Crutchfield is our go to place for wire harness print outs. And instructions for a used kit.

 

The only color matching / splicing you do when using the interface is to the back of the head unit. All the OEM stuff plugs right into the other side of the box. I've used crutchfield before for matching OEM wiring to head unit wires but not for this particular step. I actually used them for info regarding replacement tweeters in the HHR. The interface install seemed pretty self explanatory. Obviously it wasn't, looks can be deceiving, so can sound 😂.

 

Sounds good, I see you have the problem in hand , enjoy the tunes!

 

So stock radio has taken a poop on me...... so jumped and got a pioneer av120bt. The gmos lan 04. Ran it wire for wire, but car turns on to security and won't start..

07 lt, no on star, factory sub and speakers. I know this interface is used for one with installing, but I figured that didn't really matter.... im guessing it does??

Also weird relay was wired in the middle of this wiring kit.. I got the kit used,, so not sure if it is supposed to be there or not..

Relay between yellow wire and brown with white stripe.

1 yellow wire, soldered to 2 yellows.

assuming onstar plug


interface

back of head unit