Mercedes Newbie With Electrical Issues - PeachParts Mercedes-Benz Forum

LoosBenz · #1 07-08-2010, 12:47 PM

Hi All.
I just wanted to introduce myself as a first-time Mercedes owner. I've owned a diesel (VW) prior to this vehicle, but this is my first Mercedes.
It is an '87 300D (yes, with the #14 head). It runs and drives (mostly) fine, but a portion of the fuse box is dead. Anyone here have experience accessing the wiring within the fuse box?
Cheers,
Louis

Jeremy5848 · #2 07-08-2010, 08:39 PM

Please be more specific. What "portion" is dead and how do you know?

LoosBenz · #3 07-08-2010, 09:50 PM

Thank you, Jeremy, for your response. When I bought the car, the turn signals, horn, windows and seats were all inop. The way I have narrowed down the problem(s) is that after checking the fuses, I tested for voltage and there was none. Interestingly, several of the fuses had been replaced with shorter than OEM glass tube fuses at some point prior to my purchase. I have been able to restore the turn signals (if only temporarily) by using a full-length fuse. Apparently, the flexing of the upper terminal by the longer fuse returns conductivity to that terminal, so the problem is still there, just band-aided.
However, fuse positions E, F, G and H remain dead. I have been able to operate the windows and seats by jumpering (with a fused jumper wire) from position 12 (unused space), so I know everything works. There just is no power to them, presently. So, if I can get at the wiring in the fuse box leading to the fuses, I can continue troubleshooting (though I've been suspecting the ignition switch, as well). Any thoughts are appreciated.
-Louis

babymog · #4 07-08-2010, 11:06 PM

Is there power to the bottom of the fuse mounting? If not, possibly the ignition switch (doesn't need accessory power to start and run). If you just need a new fusebox, they're pretty easy to get used, same as 300E et al.

LoosBenz · #5 07-08-2010, 11:51 PM

I guess my question now would be how hard is it to change a fuse box?

The $500 300D

tbomachines · #6 07-09-2010, 12:03 AM

Very easy, open up the box lid, and you'll see the screws holding it down. Just unscrew all the screws and it will lift up--although the back portion where there are relays and stuff you'll have to unplug them from the sockets. Its a whole mess of wires underneath the box. Btw, nice buy!!

LoosBenz · #7 07-09-2010, 12:25 AM

Quote:

Originally Posted by tbomachines

Very easy, open up the box lid, and you'll see the screws holding it down. Just unscrew all the screws and it will lift up--although the back portion where there are relays and stuff you'll have to unplug them from the sockets. Its a whole mess of wires underneath the box. Btw, nice buy!!

Fantastic!
Thanks! Found it on Craigslist and couldn't resist. Yeah, you guys are dangerous. Every time I come on the forum I see something that makes me think "Ooo...I wanna do that!"

Jeremy5848 · #8 07-09-2010, 01:25 AM

It's probably not the fusebox.

Probably best to disconnect battery negative first. Then:
First, remove the fuse cover (you knew that).
Second, remove six (6) captive screws in the fuse/relay box cover. Take the cover off and you will see three columns of relays behind the fuses.
Third, remove one screw, front center, and the fuse panel is now loose (held by hooks at the rear, lift up gently at the front and the back will come loose).

As was said, there are a million wires on the underside of the fuse panel. I would not want to change one although it is certainly possible, just a lot of wires to label and keep track of.

Fuses EFGH are all in a row on the far left (driver's) side of the fuse panel. Fuses E and F both get their power from the power seat relay. Fuses G and H both get their power from the power window relay. If those relays don't have power or don't work, Fuses EF and/or GH won't get power and their loads won't work. Fuses EF power the seats. Fuses GH power the windows (you probably knew that).

The power window relay K4 lives in the relay box, behind the fuses (rearmost, center column of relays). The power seat relay K5 also lives in the relay box (right or passenger side column, rearmost relay).

The power window relay is turned on when you turn on the ignition. Fuse 2 must be good for the relay to work.

The power seat relay is turned on when you turn on the ignition or open a front door. Fuse 2 and the Power Seat Diode V1 (relay box, left or driver's side column, rearmost little plug-in thingy) must both be good for the power seat relay to work with the ignition switch; Fuse 9 must be good for the relay to work when you open a door.

Now you have some things to check! Let us know what you find.

Jeremy

LoosBenz · #9 07-09-2010, 09:27 AM

Wow! That is some GREAT information, Jeremy! Thank you for taking the time to write up such a complete description! It shouldn't take long for me to find, or at least dramatically narrow down, the problem(s). I won't be able to look at it this weekend as I will be out of town. But, upon my return, I'm actually getting excited about jumping back into it again.

There are a number of other issues, but I'm tackling them one at a time.
Thanks!
-Louis

Jeremy5848 · #10 07-09-2010, 01:12 PM

You are in a really enviable position; you can spend $5000 on that car and still have less in it than I started out with! Yes, one thing at a time. It's all fixable.

Jeremy

LoosBenz · #11 07-13-2010, 07:46 AM

Quote:

Originally Posted by Jeremy5848

You are in a really enviable position; you can spend $5000 on that car and still have less in it than I started out with! Yes, one thing at a time. It's all fixable.

Jeremy

Heh...well as you probably know, you can often spend the money for a good, clean, fully serviceable car and end up spending less than fixing up a cheap one. There were a number of "red flags" that would have, and probably did, prevent more sane people from purchasing this car. So far, I have been correct in my assessment that the issues it has are relatively minor and that with a little patience, this will be a nice driver.

The windows and seats are working again! After pulling the complete lid assembly exposing the relays, the first thing I see is a pair of fuses in a relay-type mount that are so corroded that they are white and flaky. These are not the problem, but are indicative of a moisture problem. Gonna have to work on that.

The real problem, as it turns out, was the terminals of fuse #2. I kept looking for power there and finding nothing. Apparently, I wasn't being aggressive enough with the DVM probe. After some cleaning, I could wiggle the fuse around and hear clicking from the relay. A little more cleaning and the seats/windows have been working consistently.

I still have a few more electrical items (mostly lights) that need attention. I also have to seal up a coolant leak at the upper radiator hose neck where it bolts to the head. Then, I can take her for some durability runs. I'm suspecting a weak fan clutch and am researching replacements.

Thanks for the replies. I love this car and really hope I can make something of it.

LoosBenz · #12 07-29-2010, 11:22 PM

Quote:

Originally Posted by LoosBenz

...I also have to seal up a coolant leak at the upper radiator hose neck where it bolts to the head. Then, I can take her for some durability runs. I'm suspecting a weak fan clutch and am researching replacements.

Leak repaired. Temp seems to be steady reading slightly above the 80C mark. The radiator needs to be replaced as part of the upper hose port has broken off. I still think the fan clutch is bad though I haven't replaced it, yet. But, overall, I'm pleased with how things are progressing and the car runs well.

Now for some quality time with the car this weekend.

dagObx · #13 07-30-2010, 01:15 PM

If you replace the fan clutch, use one from a 606 engine (I think that's the one). Its cheaper than the one for the 603. Also consider replacing the fan as well with one from the 606(?) engine. Did that myself & it dramatically improved air flow over the radiator.

Good luck & keep us in the loop!

sixto · #14 07-30-2010, 03:50 PM

Not just any 606. You want the clutch and 11 blade fan from a 98-99 E300. You might have to notch a corner of the... umm... turbo air inlet hose I think it is. The 606t fan setup sits further aft of the original 87 300D fan. Not a problem in an SDL.

Sixto
87 300D

LoosBenz · #15 07-30-2010, 08:53 PM

BLAST!!! Looks like my "quality time with the car this weekend" has been limited to this afternoon.

Oh well, I guess it could have been worse. The first part of the maiden voyage actually went quite well. But it did feel sluggish at first...to the point I nearly turned around and came home before I completed the first mile. Actually, I DID turn around, but it started feeling (relatively) normal so I continued on an alternate route. Transmission has the just-got-rear-ended-by-a-semi shift action, but other than that, the car drives quite nicely. No weird noises. No rattles/squeaks. Engine and driveline are smooth. Temp is staying steady. I decided to stop and pick up a couple of things for dinner. When I came out of the store, there were no puddles. Splendid!

She started right back up and I made my way back to the house. On the way back, I decided detour and turn on the street where it started feeling sluggish earlier. Aaaaand....it did it again! What the heck...and now the temp is rising. I got a little whiff of coolant, but I had already passed the road that I turned around on before. So, I had to continue to the next. As I started the turn, I smelled hot brakes...and now the temp is at 100. CRAP!

I started back and did a few speed-up, shift to neutral, shut off the engine and coast cycles. The car was rolling poorly, but I made it back to the house and parked it. A nice plume of steam rolled out from the grill. I opened the hood to see the radiator had further failed at the upper hose neck spewing coolant at the PS pump. And judging by the smell and heat from the left front caliper, I guess I'll be buying one of those, as well.

The good new is that the temp never got above 110. Looks like this first "wringing out" produced a failed radiator, a stuck caliper and a cranky transmission. Out comes the wallet. It really COULD have been worse...stay tuned...