1989 Mercedes 190 aftermarket deck probs.

Okie we did a radio install on an 89 mercedes 190 (no factory alarm).  Had everything hooked up and it worked fine, then customer comes back a day later and says it stopped working all of a sudden.  Brought the vehicle in and it's acting as if there's a speaker short somewhere.  The deck (Pioneer 4500mp) is powering up and activating the antenna and getting reception and appears to be functioning normally, it's just not outputting any sound, although when we got done doing the original install it was working just fine.

If you recall these vehicles have that stupid fader knob thing right near the gear selector in the middle console, and the factory radio only has outputs for two speakers.  Usual way of hooking up an aftermarket deck is to use the front ouputs of the aftermarket deck to the wires in the factory harness, and tape off the head unit's rear outputs.  And then for fade you continue to use the factory fade knob in the center console.

First thing I did to troubleshoot was to pull the pioneer out and check all the wires.  Good ground, no bare wires, everything is perfect.  Next thing I did was I kept the pioneer plugged in to the vehicle's wiring, but at the same time I hooked up a test speaker to the head unit's front output channels.  Note that I left the wiring into the vehicle intact, I just cut away some oof the insulation to make my temporary connection to the test speaker.  When I did this, I got output from the test speaker.  It worked on both the left and the right channels.  This leads me to believe that it is not a factory speaker wire grounding out as I had originally hypothesized, cuz the test speaker would not have received any output if that were the case (the pioneer deck would still be seeing the speaker short and going into protection mode).

So now I'm thinking it might be something with the fader control and/or the factory amps or line drivers or whatever is in there.  During all of my troubleshooting I did test the knob to see if it's position had any effect on whether or not sound was output, but it didn't affect it at all.  I'm assuming since there's 4 speakers but only two speaker outputs from the head unit, that there has to be some kind of factory amp and thought maybe it's located near the fader knob?.

The guy is coming back sometime next week and I need to know what to try next to get his system working again.  The center console doesn't look like it'll be too terribly hard to disassemble should I need to get access to that fader knob and whatever wiring lay behind it.  But it'd be nice to know if that's even worth the effort or not.

One thing I did not do was to check the fuses, in the off chance that there's an amplifier fuse or something somewhere.  These are the stupid kind of fuses that you have to use a tool to put in unless you want to risk burning the skin off your fingers (just happened to one of our guys the other day when a fuse blew as he was inserting it).  So I am trying to avoid the fuses but if it's something I really need to check I will do so.

Anyone have any ideas or bits of info they might be able to provide?  Thanks in advance.

the first thing i would check is the impedence of the speakers. if there are 4 speakers and 2 connections the speakers are in parralel or series. if you,ve had any experience with pioneer radios there is no protection in most cases the ic's burn out and the radio must be repaired. did you bench test the radio to see if it's toast?. my suggestion is this, run new wires directly to the speakers after checking to make sure they are 4 ohm anything less will burn out the speaker outputs, if not instantly - eventually. this would explain why the radio worked initially and won't now.

Hey all, thanks for the replies.  I think I mentioned this is my first post, but just to clarify, I have already tested the pioneer's outputs and they work fine.  I used a 3.5 inch 4 ohm test speaker and the output sounded completely normal, for all 4 output channels even though only the fronts are the ones hooked up to the vehicle.  So this means the pioneer radio is fine and nothing is burnt out, and I'm also assuming this means the problem is not something to do with the factory wiring giving the head unit too low of an ohm load.  I did not get a chance to check the resistance of the factory wiring but I figured the fader might interfere with that anyways and give me an innaccurate reading.

Thing is, I also tried the test speaker while the factory wiring was in place and the output to the test speaker was fine.  So if there were any problem in the factory wiring such as a speaker short, then I would think the test speaker would not have worked either.

I did not want to try and use a speaker popper on the factory wiring because I wasn't sure if this might damage the fader control, since it appears sound goes to that first and then to each speaker.  And since there's 4 speakers in the vehicle but only two sets of inputs, I knew that there had to be some line driver or amplifier somewhere and definitely didn't want to use a speaker popper on its input.

we have done many radios in these vehicles ('89 190, 2 '90 300Es very recently actually) that have the same factory systems, and have never had this particular problem happen before.  All the other stores hook it up the same way we do and they don't seem to have problems either.

But like I said I have verified the speaker outputs of the pioneer head unit and they are fine.

It sounds to me like I'm gonna have to take apart that center console to get to that fader knob and see what's going on in there.  Also, someone told me there might be a factory amp in the trunk somewhere?  Can anyone verify this?  If so, I might try testing that first cuz it'd probably be easier to get to than that fader.

Okie well whenever the dude comes back I will check the fuses, test the factory wiring for resistance, and then check the factory amp and/or fader.  I'll keep you all updated, and in the meantime any additional suggestions or info are much appreciated!  Thanks again guys.

Okie so it looks like no matter what I'm gonna have to tear apart that center console to get to that fader knob.  I guess we'll see if all the connections are okay and if it seems like the thing is just broken we'll bypass it and go to the speakers directly. And while we're there I'll test to see what ohm the speakers are.

Thanks for explaining the fader knob and how it works--very useful info for future knowledge.