H3 Help pls... Nexus7 + GMOS-04 + Headunit replacement

[nelly27281]

Hi all gurus,

I am planning to replace the stock headunit and replace it by Nexus 7.

So I've ordered Axxess GMOS-04 harness. :link:

I've connected all the wires as per the manual and got some idea from this youtube video :link:. But now I am stuck with few questions/confusions (sorry I am not electrical guy).

From the 24-pin harness (which will connect to factory harness), I am left with:
1 Yellow - 12 volt battery/constant (12v+)
1 Black - Ground

From the 16-pin harness (which will connect to GMOS-04 adapter), I am left with:
2 Red - 12 volt ignition/switched (12v+)
1 Blue/White - AMP turn on (12v+)

So, my questions are:
1. Which wire/s should I connect to cigarette lighter adapter (which will supply power to the tablet, I want to supply power only when I turn on the keys), Yellow / 1 Red / 2 Red ???
2. Should I connect Blue/White wire to the power supply wire (answer from 1) so that it will turn on the amp as soon as I turn on the keys???
3. How the GMOS-04 will retain the RAP feature in my case ???

Here is the pic which is part of my complete set up:

THANK YOU IN ADVANCE...

 

[humvee]

Started off with this project once only to find that its not as practical as it seemed in ny head.
Looks like you're half way done but...
I recommend a 7" Pioneer screen with android mirroring & apple carplay. You get your maps, contacts, messages etc.


Sent from my iPhone using Tapatalk

 

[nelly27281]

Hey Humvee
Thanks for the suggestion but as you know I'm half way done, so I've to stick to this plan...

Only the confusing part for me is this wiring...

 

[SedonaBound]

I'm no guru, but did recently install a new head using the GMOS-04 harness, so this may help:
1. 12V outlets in H3 are not switched or RAP. They are hot 100% of the time. You must use a fuse tap to put one or more of the outlets on RAP. I posted this method a few weeks ago: http://www.hummer4x4offroad.com/forum/showthread.php?9343-Simple-Switched-12V-Outlet.
2. Seems to me that you'd want the amp powered only when the source (tablet) is on. That would mean wiring the red (head power) lead from the GMOS to a relay providing full power to the outlet instead of the method in my link above.
3. The GMOS processor takes battery 12V (yellow) from the truck harness and uses the BDM data stream to determine when switch the head (red) and amp (bl/wht) on/off. In other words, it makes its own "RAP". It also passes some full time power to the head for clock and memory. If you convert the 12V outlet powering the tablet to RAP, the blue/wht from the GMOS should power the amp at the same time.

 

[nelly27281]

Thank you SedonaBound for sharing your method and inputs.

Here is the part of my setup with all the harnesses from GMOS-04.

I am not planning to use Yellow (from stock harness) as it's hot all the time.

As you can see I have 2 Red (from 16-pin harness), so should I join both the Red to Blue/White or just one Red with Blue/White and tap off another Red one?

 

[Cyouincourt007]

Bump

 

[SedonaBound]

Thank you SedonaBound for sharing your method and inputs.

Here is the part of my setup with all the harnesses from GMOS-04.

I am not planning to use Yellow (from stock harness) as it's hot all the time.

As you can see I have 2 Red (from 16-pin harness), so should I join both the Red to Blue/White or just one Red with Blue/White and tap off another Red one?

You may need to call Metra Tech Support. I have a hunch that GMOS Axxess module requires the yellow lead from the truck for full-time 12V, which is then parcelled out to the harness leads depending on the BCM data stream. They were pretty helpful for me when I ran into issues because the prev. owner had buried an iPod module where I couldn't see it and couldn't figure out why my head unit wasn't working right.

 

[humvee]

I've to stick to this plan...

True & sorry for the negativity.
Good luck with this! We'd love to see a video of the set up in action once its all done.

 

[nelly27281]

You may need to call Metra Tech Support. I have a hunch that GMOS Axxess module requires the yellow lead from the truck for full-time 12V, which is then parcelled out to the harness leads depending on the BCM data stream. They were pretty helpful for me when I ran into issues because the prev. owner had buried an iPod module where I couldn't see it and couldn't figure out why my head unit wasn't working right.

I already tried, I guess they don't have any idea about this kinda setup or they may be afraid to give wrong info.
Anyway I'll give it a try in my way this weekend. Praying I won't get smoke out of any part.

 

[nelly27281]

True & sorry for the negativity.
Good luck with this! We'd love to see a video of the set up in action once its all done.

Sure, I will share the whole setup as soon as I'll make it start working as I've expected.
Thank you for the wishes.

 

[Graham2990]

How do you intend to mount the tablet in the stock location?

 

[nelly27281]

How do you intend to mount the tablet in the stock location?

I've ordered Metra's double din installation kit from Amazon. You'll have to use your dremel skill on it though.

 

[humvee]

I've ordered Metra's double din installation kit from Amazon.

What functions would you lose or retain with this setup? (battery chimes, etc.)
Do you have the monsoon sound system on your 3?

When you get this done, I'll revive the project and put an iPad mini in there the next day.

 

[nelly27281]

What functions would you lose or retain with this setup? (battery chimes, etc.)
Do you have the monsoon sound system on your 3?

When you get this done, I'll revive the project and put an iPad mini in there the next day.

Metra's kit is to install any after market double din stereo. It will just hold the stereo.
You'll also need Metra Axxess GMOS-04 (for monsoon system) or GMOS-01 (for NON monsoon system). This is wiring harness which will connect your stock radio wiring to after market stereo. You can simply splice the stock wires and connect, but you'll lose other features. This harness will retain all the feature like on-star, chimes, etc. And if you change your mind you can unplug the harness and go back to stock.
You'll also need antena adaptor.
I've whole list which I'm going to share in my next thread after completing the installation.

 

[nelly27281]

Ok, so I was very close to finish the setup, but when I hooked up everything just to test everything is working properly, it turned out the audio was very low. You can say 1/4 of the stock radio sound.
I basically connect audio output wire from tablet to the speakers wires from GMOS and turned the blue screw on GMOS all the way clockwise.
I've googled for other install and found out everybody is using DAC in between them, I've ordered one to see if it help.

Any thoughts on this...?

 

[Humvdood]

Ok, so I was very close to finish the setup, but when I hooked up everything just to test everything is working properly, it turned out the audio was very low. You can say 1/4 of the stock radio sound.
I basically connect audio output wire from tablet to the speakers wires from GMOS and turned the blue screw on GMOS all the way clockwise.
I've googled for other install and found out everybody is using DAC in between them, I've ordered one to see if it help.

Any thoughts on this...?

Hey, just now seeing this post...
Are you using a headphone jack or a bluetooth module to carry audio signal?
If you already have the bluetooth module, I would feed it into a preamp with decent wattage to get some power to your speakers.
If you're just running straight from the bluetooth module to the speakers, they're going to get very weak signals.

I do ipad installs professionally - if you like I can draw up plans on what I would do for an h3 and you can see if there's anything you can add or take away to boost sound quality without spending a crapton of money or changing up what you've got going so far.

 

[Humvdood]

nevermind, I see where you're using the headphone jack and splitting it to the speaker signal wires - that won't give it enough power - give me an hour to draw something up with a small amp or something you could cram in there

 

[nelly27281]

nevermind, I see where you're using the headphone jack and splitting it to the speaker signal wires - that won't give it enough power - give me an hour to draw something up with a small amp or something you could cram in there

Awesome, thanks a bunch Humvdood...
Just FYI I've monsoon system so it comes with amp.

 

[Humvdood]

Awesome, thanks a bunch Humvdood...
Just FYI I've monsoon system so it comes with amp.

Hmm... that does kind of change up how I would approach it.
Most stereo head units put out around 120 watts to the amp - the amp then... you know... amplifies
tablets and phones put out like 30 milliwatts which... math... is way less signal to amplify
you need something to boost that initial signal if you're feeding it into the amp.
I would feed from that 3.5mm headphone jack to a 4 channel mini-amp or even a 2 channel and combine the signals.
you shouldn't need much - I might even suggest something cheap like a motorcycle amp for around $20 on amazon. put it between the tablet and the gmos unit.
some stereo guys might freak out and say you're going to blow that gmos unit but get something with low wattage like 100 to 300 watts (comparable to head unit wattage) .
you could try a DAC and see if they have one that amplifies signal around that wattage but I was trying to keep it on the cheap and easy for you.

Most of my installs run to an aftermarket stereo - even like a cheap pawnshop stereo just so you've got radio and a something to process that initial signal.
I've been happy with my kenwood and dvd monitors but you've got me wanting to put an ipad in my h3 now :wink:

 

[nelly27281]

you could try a DAC and see if they have one that amplifies signal around that wattage but I was trying to keep it on the cheap and easy for you.

Well I've ordered Behringer UCA202 Audio Interface, just waiting for it to arrive and test it with my setup.

I've been happy with my kenwood and dvd monitors but you've got me wanting to put an ipad in my h3 now

I thought of iPad first but then I compared the sizes of iPad and Nexus 7 (2013 edition), it turned out Nexus 7 fits perfectly in Double Din kit from Metra and that will replace the stock radio. Nexus 7 has crispy display and latest android and it supports OTG (On-The-Go) cable, so charging plus external storage which is a great idea.

 

[SedonaBound]

Some suggestions:
Did you do the chime adjust and amp adjust in sequence per the Metra instructions? I believe you need to go through both in sequence, else the Axxess processor thinks you're only setting the chime level.

If you hear music, the raw file is already converted to analog; which is what a DAC does. I don't see what you'll gain adding a DAC unless you're going to use USB for output and read the raw files. A DAC won't boost line level to the amp.

How do you have the output connected to the eight wires in the harness? I'm curious how you get four channels from a mini-RCA jack. Does the tablet output have a fader function; i.e. are there wires for L/R front and rear?

I looked at few reviews of the Nexus 7 that said the audio output level was very low, so that may be the root of your problem. If all else fails, see if you can test it with a different tablet or a laptop.

 

[nelly27281]

Thank you SedonaBound for your suggestions.

Some suggestions:
Did you do the chime adjust and amp adjust in sequence per the Metra instructions?

I did this adjustments in sequence, but I'll double check on this.

How do you have the output connected to the eight wires in the harness? I'm curious how you get four channels from a mini-RCA jack. Does the tablet output have a fader function; i.e. are there wires for L/R front and rear?

I am using 3.5 mm to RCA cable. I splice the RCA ends and connected the Red (from RCA) wire to right side speaker wire and White to left ones. I've joined front right and rear right together and same on left side, so I am getting only right to left and left to right fade. I am not worrying about front to rear and rear to front fade.

I looked at few reviews of the Nexus 7 that said the audio output level was very low, so that may be the root of your problem. If all else fails, see if you can test it with a different tablet or a laptop.

I doubt on this one as I've tried to play music from my phone as well and it gave same output.

 

[SedonaBound]

Thank you SedonaBound for your suggestions.


I am using 3.5 mm to RCA cable. I splice the RCA ends and connected the Red (from RCA) wire to right side speaker wire and White to left ones. I've joined front right and rear right together and same on left side, so I am getting only right to left and left to right fade. I am not worrying about front to rear and rear to front fade.

I think there are two problems. First, you're trying to drive an amp looking for much greater pre-amp level than a tablet, with output in millivolts meant for ear buds, can provide. Second, you're paralleling each channel output into two (F/R) channels which drastically cuts the already weak level to each amp input. Have you tried it with the tablet output driving only the F or R amp inputs? You may get enough level, but distortion may also be high with the level cranked high on both the tablet and the Axxess module.

I think you need a pre-amp that converts 2-chnl (L/R) from the tablet into 4-chnl (FL/FR/RL/RR) at a level appropriate for the amp. The Berhinger unit is still two channel. Suggest you call Crutchfield or a car audio specialist who's familiar with the hardware.

 

[nelly27281]

I think there are two problems. First, you're trying to drive an amp looking for much greater pre-amp level than a tablet, with output in millivolts meant for ear buds, can provide. Second, you're paralleling each channel output into two (F/R) channels which drastically cuts the already weak level to each amp input. Have you tried it with the tablet output driving only the F or R amp inputs? You may get enough level, but distortion may also be high with the level cranked high on both the tablet and the Axxess module.

I think you need a pre-amp that converts 2-chnl (L/R) from the tablet into 4-chnl (FL/FR/RL/RR) at a level appropriate for the amp. The Berhinger unit is still two channel. Suggest you call Crutchfield or a car audio specialist who's familiar with the hardware.

Thank you SedonaBound...

I am thinking of small 4 channel amp and I'll contact Crutchfield to get their inputs, will keep you guys posted.

 

[nelly27281]

My question to all is this guy has installed Nexus 7 in his car dash.
He also have Bose system (like I do) and he has same setup (like I do).

Now the question is why he is getting proper audio volume and I am not...?