Cautiously Optimistic
 

Ok, I took the connector closest to the gas pedal apart and cleaned it all up and reassembled it. I popped yet another fuse in the socket and drove off with my fingers crossed! At roughly the same place (speed & distance) I applied the brake and 1 or 2 seconds and pop goes the fuse. I thought, what the cuss!! So, I go back and I decide to unplug the other connection (the one that's about 4-5 inches away towards the rear of the car). I put in yet another fuse and head out. I tried everything and could not get the fuse to blow!! So, is this a victory of some sort? What is this connector for and where do the wires go?? Anyhow, my fingers are still crossed!!

Can you take a picture of this connector, I'm not picturing its location for some reason.

A pic w/ a brief description of wire colors, since they don't always come through. Quantity of pins, would help too.

Connector Photo
 

Here's a photo of the connector. The connector with the brown gooey stuff is the one on the left with the purple wires. The one we are talking about now is the one that is unplugged on the right side if the air duct and center of photo.

It is a 8 pin connector wires are as follows:

Top row from left to right - Blank, Red, Red w/white stripe, Brown
Bottom row from left to right - Gray w/purple stripe, Brown, Red w/black stripe, Red w/yellow stripe

JamesDean, how do you post those great photos? Obviously mine didn't come out very big!

Is that the connection for the hazard switch? If so, that's between the fuse and the rest of the circuit. It might not be real helpful for tracing it down, since everything downstream could be the cause. E.g. the hazard switch in the console, or the wiring up to the flasher relay behind the cluster, or the combo switch...

Page 2 in the pdf

Do you turn signals work with that unplugged?

I thought that might be for the brake lights. Check them as well.

No Luck!!
 

So, I took the old girl out for a spin this morning with the same connector unplugged and it would not blow. So I plugged the connector back together and within a couple of brakings from over 25-30 mph it blows. I pull over put in another fuse and unplug the connector. I take it up to 40 and make a hard full stop and the damn thing blows!! So, I'm lost in space again. If I can't replicate without going to speed and braking to a stop, is there a way to use the meter on anything? I've been scratching my head and just can't see a way through. Any thoughts??

Okay, matching your description of the connector up, that's C107 and is for the power windows. There's an error in the FSM in the back that ID's this as a 6 pin, it's an 8 pin. You could (if you cared) check pages 130-131 and see that the 7 wires match.

There's no connection between this connector and Fuse 12, so its earlier behavior was a red herring.

Have you disconnected the cruise control switch on the column?

You may also want to remove your instrument cluster and check that out for burned traces.

Can you actually see when it blows via the gauges failing since they're off the same fuse? [Watching your cluster while braking is not a great idea, so you might want an assistant so you can watch the road.]

I would also check brake fluid, and the brake wear sensors. There's a path through to ground via the brake fluid level sensors. If they're low, and the problem occurs under hard braking, maybe it's there. Likewise with path to ground via the wear sensors.

You might also try removing the hazard switch from the console. In theory this should isolate the turn signals from fuse 12. You'd be without signals, but that would mean you drive like other idiots who don't use them.

Another option might be to unplug the warning module (like a relay). This, in theory, should isolate the warning lights, the alternator, and maybe some other things from fuse 12.

Continuing that idea, proceed on to the Top Dead Center amp (?); then maybe the cluster itself. I don't know if you NEED a TDC amp to drive, maybe just for the tach? Maybe not speed, but RPM related? Sheet 4 on the pdf.

Thanks for the input Yak
 

It is true that connector was for the power windows. I looked at pages 130-131 and I'm not sure that I fully understand. Is that connection shown? I see everything else and the wire colors are the ones I noted in the connector.

Hello Yak and thanks for the input!

Yes, when the fuse blows the instrument cluster gauges all fail as expected.

I just disconnected the cruise control switch on the column.

I removed the instrument cluster and diddn't see anything there but I completely disconnected it.

I topped off the brake fluid as suggested. the little rubber covers on top of what I guess are the two sensors are all cracked and split but the fluid level is good.

Then I took it out for a spin and some hard braking and the fuse blew again.

I disconnected the brake fluid level sensors.

I disconnected the front brake pad wear sensors.

I disconnected the warning light flasher switch.

Drove around and the fuse blew again! Seems like we are running out of options.

I looked in The FSM but really tell where the TDC Amp is to disconnect.

How does one know if a TDC amplifier is malfunctioning?

How does one know if a brake sensor is malfunctioning?

How does one know if the sensors on the brake fluid are malfunctioning?

Seems like we are running out of options?? Could it possibly be the brake light switch? I kind of thought we ruled it out earlier but I'm just wondering.

See that little number C107 on/next to the wire paths? That means "connector" between the lengths of wire. That's useful info if troubleshooting. In the back of the electric section of the manual it tells you where those connections are located, with [crappy] pics.

You can also go backwards, "I've got a 14-pin connector in the LH footwell...what's it for?" but it helps if the FSM is correct. In the case of the windows, it's not and IDs that as a 6 pin in the back.

Well...if they cause the fuse to blow, they might be malfunctioning. Sorry.

I assume the TDC is for the tach. On the page where the diagram is, it says for locations go to 217. So you go to 217 in the manual, and it says "TDC Amp...in cap of diagnostic connector...202-2" so you go to page 202, look at pic 2. It shows a pic of the left side of the engine.

I think the diagnostic connector is the round screw cap. I never had any call to mess with it. The book says the amp is in the cap.

I'm running out of ideas to suggest. If it's speed/motion/rpm related, then that may be a loose or chafed wire somewhere on the F12 branch. Since the F12 is the switched fuse, it's possible that someone hacked into it for a aftermarket radio or something.

Crazy question:

Has the brake light wiring been mucked with? any of the wires damaged? On some cars I've seen, the tail-light wiring passes under the side plastic panels in the trunk. Maybe one of yours is getting wet somehow, or maybe the wires have been crushed? Something to check.

Progress Report
 

I have a progress report. First, thanks to all for the ideas and input so far. The process has taught me alot and has been very helpful. I had to leave for a week and I'm ready to get back into it. I refuse to let this thing win!!

I tried to get the fuse to blow by making a abrupt stop with the ebrake and could not. So then I unplugged the brake switch at the brake pedal and could not get the fuse to blow. With this and all the other tests and observations I have concluded that the problem has to be in the brake switch itself or a damaged wire going to the tail lights.

I took the tail light assemblies apart again and made absolutely sure there is nothing causing the problem there.

Any ideas where I would start to look for problem wires? The trunk section is fairly easy to access and the places under the dash are easily accessible with it taken apart the way it is now. But after that would I need to remove seats, carpet etc.? Do the wires to the tail lights run all inside the car?

Any words of wisdom on this next undertaking?? Thanks again to all!!!

Craig

Since it appears to be speed and/or motion related, I'd look at places that get pinched or move. Because it isn't replicated by using the brakes when not moving, I wouldn't place all the eggs in the brake circuit basket, but you've got to start somewhere.

I'd trace back from the brake lights. Look for where the harness goes under the sheet metal panel near the fuel tank. Look for where it passes under the seat. If there's a place where it flexes, maybe it's chafed inside.

Or start at the fuse box and go downstream.

Carpet and seats are easy to remove.

Like I said in reply #65, the wires to the tail lights pass UNDER the two side pockets in the trunk. I've seen 2 cars, a 190D and a 300SD that had issues with the wires being chafed. The side panel just pulls out in one piece. Easy check.

Hello Holmesuser01 and Yak, I pulled the trunk panels out and looked at all the wiring in the trunk and there is no obvious signs. I took the rear seat out and didn't see anything there either. Tomorrow I take the front seat and carpet out and have a look. If I don't find anything I think I'll string some temp wires to the lights and see if I can learn anything. Just seems like it has to be from the brake pedal back because it won't blow the fuse with the brake switch disconnected. But what do I know!! Thanks for the input.

I dont believe its your brake lights. I also dont have any other ideas at the moment.

When your brake lights are active they draw about 5 amps total or more if you have other lights wired in (fog light brake mod). Which is more than 50% of the 8 Amp fuse's capacity.

That leaves 3 amps left to whatever else is on the circuit. 3 amps for all the normal mercedes things. Now if something is amiss and is drawing more than 3 amps, when you add that extra 5 amp load, its going to pop the 8 amp fuse.

If you apply the brakes while parked and they don't blow the fuse then I don't think there's anything wrong with the wiring for them as none of that moves during transit.


I'll look back at the FSM and see if I can see anything else.

FSM Lists:

Stoplights
Cruise Control
Warning Indicators
Gauges
Turn Signal Lights
Warning System

Have you checked out your turn signal lights? What about the turn signal switch itself? Does yours function fully?

If you were adventurous, you could connect up the meter to the fuse as we did previously and drive the car around and see what happens. I suppose you could also jack up the rear end of the car, safely secure it and "drive" that way. Aside from bumps that would be pretty much the same...

Hi JamesDean,

Well, I believe it's not the turnsignal switch because I disconnected the combination switch at the steering column. It was one of my original suspects because it was replaced a few years ago and every now and then the wipers would come on and make one swipe.

Last week I was driving the thing around with all of that FSM list disconnected. Literally the instrument cluster out, cruise control disconnected, warning stuff disconnected, brake sensors and brake fluid sensors disconnected. Almost like everything disconnected and still be able to start the car!

Then my last thing was, I disconnected the power to the brake light switch and could not get the fuse to blow.

Also, keep in mind not only does it blow an 8 amp it blows the 16 amp.

The FSM shows a wire going to the Cruise Control Amplifier and a wire going to the Cruise Control Actuator. But if a guy has both of those disconnected you would think they would not be part of the issue.

Then all there is from the brake light switch is the brake light switch itself and the lines to the brake light assemblies.

I'll take your input and do some more stuff today. It would be interesting to see if it would blow the fuse with the back jacked up. Because it does seem like it needed that forward momentum coming to an abrupt stop to make it blow.


Onward I go! You have shown me that I can always convert it to a recliner!!

I'm keeping my fingers crossed for you. Electrical problems can be misery to find.