94 E500 SOUND AMPLIFIER MYSTERY WIRE

[rinconmann]

What is this wire from battery to AMP? There are 2 AMPS in my 94 E500 and both were replaced at a local stereo shop with "used" (more like defective) a few years ago. I never saw their work until today and don't think this is stock wiring. I want to put everything back and can only assume this hot fused lead was put in by the installer who sold me the used amps. Perhaps the used amp he sold me did not work properly and therefore he had to wire a hot lead? I thought it was a switched signal from the head unit? I have a 1492 Becker head unit and 2 amps that are Becker units 124 820 17 89. The idea of a hot lead all the time to the AMP does not sit with me. I have searched the electrical section and wiring diagrams but they lack the pin out detail of the amps. I disconnected the lead from the battery and put a wire tie on the end. No sound anymore now. Notice the in line fuse. Is this a bad amp that the installer just worked around? Maybe the relay within that switches power is bad?

 

[Maui]

Well, I hope the shop didn't use house wiring with a wire nut.

 

[gsxr]

Appears someone tried a Rube Goldberg band-aid of sorts, by adding an always-hot wire directly to the amplifier harness. You'll need to do more investigation as to what the true fault it, my guess is either the 1492 head unit, or the amplifier(s).

You may get a clue as to what's going on by identifying the wire color that is being powered, and looking at the schematic in the ETM to see what exactly that wire is.

 

[rinconmann]

Thanks Dave. So Rube Goldberg huh? Thought as much. He likes to leave parts out of cars too as I have discovered doing my resto. Makes you never want to bring your car to anybody, ever.

Stereo work around here gets sub contracted by the MB dealer so I was lost to the wind on that car and went local. That shop gave me the creeps; In fact the night they brought my car back to my house (weird in itself) and I left it out of the garage, "someone" tried to rip it off, defeated by the simple ignition lock out which happens when you use the wrong key. Bad memory.

Anyways, can you be more specific on ETM? I have a schematic for the 1492 Becker head unit so I can use.

The car has no sound since I took off that bad hot lead. You mention head unit? The head unit I am using is a "used" one from "Rube Goldbergs" shop. The unit immediately had volume control issues but fact they had it for sale perhaps tells me it had other issues. Anyways sent my orig 1492 to Becker to replace the volume potentiometer and to add an aux in so maybe all will be solved with changing that out today. I hope so as electrical can turn into a nightmare.

FYI the color line they broke into appears to be a solid red. Anybody know the source of that off hand and it comes from the head unit?

 

[gsxr]

The late model diagrams are not indexed well in the CD-ROM. See the bottom link here, named "Index (Model Year 1993 and on)":
http://www.w124-zone.com/downloads/MB CD/W124/Index/Groups/24ElectTrbleShting.htm

Then, on page 4 you'll see "Radio MB with Sound System - Model 124.034/.036 (optional on other models)", is job 82-49.00

These exist on the CD but are not indexed or linked, so you have to find them the hard way. Direct URL to 82-49.00:
http://www.w124-zone.com/downloads/MB CD/W124/w124CD1/Program/ETM/24824900.pdf

Here you'll see the amps are N40/1 and N40/2 and the red wire is fed by fuse #9, through connector X1/5. I'd start by checking that fuse and see what else it feeds.

 

[rinconmann]

So close but defeated. So I removed that wire, plugged my rebuilt 1492 Becker Head unit in and wow everything sounded fine until I started to test all the speakers and found that the passenger door speaker was not working. I noticed the antenna stopped working as well when I removed that mystery hot wire. Should have left the thing alone. Since I had 2 BAD AMPS I thought maybe the AMP was going bad or had some issue with that one speaker channel. Without recalling what was wrong with my original amps I decided to plug them in and see what happens (famous last words). NOW my existing AMP appears dead. Radio gets power and turns on. CD player changes CD. No sound. What are the chances that my AMP goes bad just switching it out with others. Either way Look s like I have to spend $150 each and send to Becker my 2 amps to rule out anything else esp. when it worked this morning (albeit missing the door speaker on passenger side). Very frustrating.

 

[rinconmann]

Good timing. Wow fuse 9 was out. I could barely see it. When I replaced it sound came back again using my old working AMP. Except the passenger speaker. So at least I am back to start. One of those bad amps must have fried the fuse. I assume Becker will check all the channels if I send an amp in? I will check the speaker to make sure it works 1st.

 

[rinconmann]

Maybe I should just buy 1 or 2 ebay jobs and solve that way?

 

[rinconmann]

Thanks again to gsxr for the detail nobody else can find and another mystery solved. My AMPS are fine. I have never had a speaker go bad except now. So much progress thanks to forum.