w126 questions

[ned2683]

i read somewhere about by-passing stock fader, and how it is only allowing 1/2 the power. how do u do this and what good does it do? are the systems in these cars 8 ohms? or 4 ohms like normal cars? my last car i ran new wires so i didn't concern about this. but i'd like to skip all the trouble and just use existing wires.

[SCLJA]

what year is your 126?

[ned2683]

1984, 300sd

[SCLJA]

It should be fairly easy on an 84> You need to dissassemble the console and get to the fader control. Then you need to cut back the vinyl tubing on the fader harness back far enough to where all the factory splices can be found. It is best to have 9volt battery and locate the 4 pairs of speaker wires by hooking up the battery across the wires till you hear a speaker pop then extend the wires to the new radio. Remember the fader control only uses the 6 positive wires and all the left side negatives are hooked together and all the right side negatives are hooked together. There are 2 positive inputs to the fader and 4 pos outputs and a total of 6 negatives also. I hope I didn't confuse you let me know if I did. Good luck Scott@lajollaaudio

The fader takes a 2ch input and supplies 4 outputs. Most headunits available these days have 4ch output rather than the 2ch like the original units.

My DPO (dumb previous owner) had put a very nice Clarion head unit in and just wired it to the fader as per the original unit, using just 2 channels, leaving 2 channels unused.

Rather than just bypass the fader I laid new cable to all the speakers directly from the head unit. What a big difference going from 2ch with average cabling and loads of joins, to 4ch and single runs for each speaker with no joins using good quality cable. The sound even using the factory speakers is awesome.

For the fronts, which are the easiest, I used a coat hanger and gently fed it down through the speaker openings on the dash until I could see the coat hanger underneath, then I simply taped the new leads to the coat hanger and pulled them back through.

To get that far you need to have removed the panels underneath the dash and also the centre console side panels to allow you to access the back of the head unit area so you can route the cables through under the dash and connect them to the head unit.

For the rears, remove the plastic sill plates on front and rear doors on one side of the car, and pull the carpet panels and you should see a cable route that runs front to rear. Pull the rear seat and you should be able to run the cabling back to front, either going across the floor or up and under the dash (best option) and behind the head unit again.

If you are pulling the rear seat and rewiring the rears you might consider laying power and additional cabling to support amps, subs, and changers. Easiest to do it once.

I am replacing my fader with a central lock switch so that I can lock and unlock all doors easily. I have a factory W140 switch that fits right in the opening.

Matt.

[ned2683]

thxs for the reply. i use to wire my other car like that. but on that car i didn't spend a lot of time going under the dashes and such.

i am a lil confuse on the point: if i bypass the fader will the 4 ch from my head unit control 4 ch of the speakers? or do i have to lay down new wire for this to happen?

If you run 4 pairs of wires to the fader you will be able to bypass the fader and wire into the front and rear speaker wires. This will make a difference however the factory wiring isn't the best quality and if you have the time and ability it's worth rewiring directly to the speakers themselves.

Matt.

[goldstone]

I'm only responding to second the advice Mattman has given.

I recently did the same thing in my 126 as he did: installed a new head unit with an internal 4x25W amp, ran 4 sets of speaker wires directly to the speakers bypassing both the fader and the two stock amps located behind the backseat. Results: Spectacular! Huge improvement in audio.

The only thing that I did differently than Mattman was to route all four sets of speaker wire back to the stock amp location (I got there via the center console, under the back carpet, and then under the backseat. Since wiring for all drivers meets at that particular point, it was a breeze to tap into the speakers from there.

I've been wrestling with whether to upgrade my speaker system; but honestly, the vast improvement I've experienced just from the aforementioned rewiring has brought so much life to the stock speakers that I'm hardpressed to go to the hassle.

How did you get under the rear carpet like that Goldstone?

Cheers
Matt.

[goldstone]

Good question: I had to innovate!

I first cut an appropriately measured length of 1" PVC pipe. Next, I worked this tube under the carpet from the backseat side, along the right side of the hump, and up to an opening in the carpet located just a few inches in under the rear of the center console. (I'd already loosened the center console to ease getting the new wires from the head unit to that point.)

From here it was simply a matter of sliding the relatively stiff speaker wires through my makeshift PVC "tunnel", pulling the tube back out, making the required connections, and reassembling the car

NOTE: The toughest part about this method was figuring out how to correctly reassemble the cable-assembly that opens and closes the fresh air vent on the center console. (As soon as you loosen the back of the console, this "Rube Goldberg"-inspired setup comes apart.) I've had my console apart before (installing a cell phone car kit last year), so I knew the procedure. I was able to get things back together in minutes; but that wasn't the case when I installed the phone last year. Then it took a LONG time for my pea-brain to figure out the procedure.

hehe, I have heard that the air vent can be a hassle. The side routing option is also reasonably easy to do, probably takes longer than your option but there's no hard reinstall for the first timer.

Cheers
Matt.

[goldstone]

I agree that the side route is probably just as good.

My only concern comes from other posts in this group advising avoidance of power-carrying conduits, given the possibility of noise/interference such proximity can introduce into the system.

I don't know if this issue is really all that relevant, but the area behind the false floor in the passenger's footwell is like Grand Central Station for the airbag, alarm, blower motor, and BenzMac only knows what else!!!

With this in mind, I opted to run my wires directly down Broadway instead!

Regards,
Eric