W140 Radio Head Unit Change
 

OK guys, I've done a search and read the numerous posts about changing the head unit in a W140. Some talk about ripping everything out and replacing with new amps, speakers, etc.
Others mention changing unit and bypassing amps, etc. Some mention running extra leads to the antenna circuit to turn on the amps.
Confusing.
I've got a 1996 S500 Coupe with the factory Bose 11 speaker system. I like the way it sounds so don't want to change the install other than the head unit.
The original head unit, of course, is AM/FM/Cassette. (M-B, what were you thinking???) I want to replace with an new Alpine AM/FM/CD/MP3 unit that's XM ready.
According to the Soundgate web site, all that's required is to use their OEM4A interface box between the new head unit and the factory wiring harness that's already in the dash.
Has anyone done this? Is that all that's required?
Thanks, KenP

Anybody?

MP3 and XM radio weren't around in 96 (not released yet anyways), and you could get a trunk mounted CD changer.

Hopefully Cleeve or Scott will have a good answer for you.

Still looking for somebody who has done this.
Thanks, KenP

I don't think your currect setup is much different that what I "HAD" in my 94 E420. Look at some of my old posts on this issue. I ordered an MCLASS connector from BECKER and made my own harness using the Alpine connector that came with the 9815 I installed. I also needed to buy an antenna adapter.

Once installed, I bypassed the factory amps by unplugging them and then running jumpers between the input and outputs. I may have documented them in a previous post.


Willy

Do you have to bypass the factory amps or will they work with an aftermarket unit?

Scott from LaJolla recommended to me to bypass the factory amps. You can stil use them, but you'll need to run the amp trigger wire to the amps to the correct pins in order for the amps to power.

If you just leave it as is, you'll get sound with radio in FM and AM mode (ie.. only when antenna is up), but not in XM or MP3 mode, as I believe that the amps are currently wired to the antenna trigger.

By the way, the METRA - 70-1784 harness adapter made for the 1987-Up Volkswagen "MAY" also work. You 'll have to check it out. I do know that the "MCLASS" adapter from www.beckerautosound.com will definately work.

Thanks, but...
 

WJM, thanks for the response, but still looking to answer the original question...
Has anyone tried to use the Soundgate OEM4A adapter between a new head unit and the original wiring?
Certainly, I want to use the M class adapter from Becker, but do not want to bypass present amps or anything else.
Not interested in running extra wires, bypassing circuits, etc. Want to leave it as stock as possible.
Thanks, KenP

Ken,

All 94-97 Mercedes (per Becker website) have the DIN-ISO connector. See: http://www.beckerautosound.com/1492.html

The antenna trigger from the stock radio powers both the amps and the antenna. That's why the antenna is up on all modes.

Most new radios have separate antenna and amp trigger wires. Antenna trigger is "ON" when radio needs the antenna (AM/FM modes only). AMP trigger is on whenever radio is on (ALL MODES).

So, now think about it. The current harness that plugs into the stock radio will accept only one trigger wire from the new radio (either the AMP trigger or the Antenna Trigger).

If you hook up the antenna trigger, you'll only have sound when the radio is in AM/FM mode, because amps will not power in other modes thus no sound... trust me.. learned this the hard way. If you hook up the AMP trigger, then you'll have sound in all modes, but your antenna will stay up whenever radio is on (even in CD, MP3 and XM modes).

I think the latter is the best solution for you. Then later (if you want antenna to go down when it's supposed to), you can run a wire from the new radio's antenna trigger back to the antenna. Disconnect the trigger wire from the antenna and connect this new wire. Should work like a charm.

I looked at the Soundgate website and do not understand how that incorporates into the system, so you may have to call them. It does not look like it takes the mercedes trigger issue into account.

Sorry for being dense and late to the party. I'd like to put an MP3 capable head unit in my 95 S420.

- Will any unit work if I want to keep the factory amps in the loop or do I have to somehow wire RCA outputs to that ML adapter?

- Are there aftermarket units that will control the factory CD changer?

Thanks,
Sixto
95 S420
91 300SE
87 300SDL
83 300SD

I put in an Alpine CDA-9815. Yes, just about any unit will work. RCA outputs are not used if you want to use factory amps.
Hmm... possibly.. but I don't think so. If you are looking for an MP3 capable head unit, why not get an MP3 capable changer?

Thanks for the response. Some follow-up:

- So speaker level outputs go into the factory amps?

- An MP3 head unit is good enough for me. I was just curious to know if I could keep the existing changer functioning without much work.

Thanks,
Sixto
94 S420
91 300SE
87 300SDL
83 300SD

Yes, speaker level output would run directly to the amps.

I bypassed my amps. I did this by unplugging both of them. THen on each plug harness, I jumped the following wires:

Input Output
3--> 4
5--> 2
7--> 10
9--> 12

I'm not sure what head units out there will control the stock changer.

I made the following spreadsheet to help me with my install.

All normal disclaimers apply.

Thanks
 

Willy, thanks for the notes and background.
Like you, when I prowled the Soundgate website, it wasn't clear which issues the adapter resolved and which it didn't...
I suspect its a line level adapter... letting the installer change the output levels of the head unit so you don't overdrive the factory amp(s)... but, not positive about this. That's why I was looking for somebody who may have bought one and tried it.
Good background on the antenna switch. Much appreciated.
KenP