93' 300E Low Oil Indicator light on....and more
 

Thank you for such a great forum! I would like to introduce myself, my name is Andrew Montoya and I own 2 Mercedes. I have just recently purchased a 1993 300E in great shape, smooth idle and no warning lights on, with 88k miles and only small details to address.
My first problem occured when I was changing the oil this past weekend and I noticed 3 wires that run parallel to the oil filter housing that were cracked and stripped. These wires seem to start at different locations from under the oil filter housing and they all end up in a plug that is secured by 2 screws in front of the fuse box. I did my best to use electricians tape and plastic tubing to isolate the 3 stripped wires but now the oil pressure indicator gauge in the dashboard is not operating (I must of done something wrong!). Also the low oil level light is coming on which is worrisome, although I check the oil level continously and it is OK. Does this light come on due to the oil pressure gauge not working? Or is it possible that this light is triggered by 1 of the 3 stripped wires? What is the best way to replace these wires and or should other components be checked. As I stated earlier, the car had no warning lights on and all was working properly. Thanks in advance for all the help...

Andrew Montoya
Orlando, Florida USA

Let me see if I can help you with this:

I had the same issues with "toasty wiring"...specifically the ones you are talking about. The previous owner apparently tried to fix this haphazardly with electrical tape, but a lot of bare wire remained.

I went to the dealership parts dept, and was told that they only sold the main harness, not the anciallary one.

So guess what? I ended up MAKING one! :rolleyes:

I have several rolls of automotive wire and heat shrink tubing.

After I completely removed the offending harness from the engine compartment, I took it in the house and measured off same length wiring of the same colors and made new wiring, and spliced the original connectors onto the new wiring.

Now the original was actually same color insulation with different color stripes (can't find that anywhere), so I just used wires with the same color insulation to easily identify what went with what.

Upon reinstallation, everything worked...except the oil pressure gauge, which just pegged at the "3" position. I had to replace the oil pressure sender a week later and it works fine now.

I will say this. There are three wires in the harness. One is for the starter solenoid, the other two are for the oil level sensor and the oil pressure sender.

Until you get that harness rejuvinated, your indicators aren't going to work very well (or not at all.

Hope this helps.

Thanks G-Benz! How hard is it to remove the offending harness from the engine compartment? Did you have to lift the car? What tools do you need to have to attach/detach the wires from their components? Have a great day!

The solenoid connection and senders are underneath the car...you will have to jack up the car to get to them (and remove the panel of course).

The solenoid ground connection is held onto the starter with a small nut. That will of course have to be removed with a wrench. It's pretty tight in there.

The other connections are the plug-in types...you just pull out. The oil pressure sender connection will probably be fairly brittle due to all of those years of heat exposure, so some of it will fall apart in your hands as you remove.

The oil lever sender is bolted to the oil pan, while the pressure sender sit up near the oil filter...a bit difficult to reach from under the car, but impossible to get to from the top of the engine.

The harness runs from beneath the car through a holder fastened near the top of the engine (I forget where). You will have to remove the wires from the assembly behind the firewall to get the harness off, since the holder diameter is smaller than the sender connections.

The wires are linked in a black box behind the firewall. I think you know this.

The hardest part of the job is getting the wires from the back of the firewall to the front. They kinda run towards the center near the wiper assembly, then out to the engine on the other side. Small hands are your best tools here.

Other than the wrench to disconnect the solenoid wire and the screwdriver to undo the terminal ends near the cockpit side, there are no other tools needed to do this.

Disconnect the battery as a precaution before starting this procedure. And due to the age of your components, take your time to avoid as much damage as possible. Stuff WILL break unfortunately (holders, grommets, etc.), but nothing that will affect the operation of the vehicle.

O.K. I took a look from underneath and was able to locate the origin of the 3 wires... my question now is: should I also change the sensors that clip on to the oil pressure sender and the oil level element? What are these sensors called? I can't seem to find them as a part on the various part websites...
Andrew.

I would not change the sensors until you have refurbished the harness...you may be getting false signals right now as a result of the bare wires making contact with each other.

If you are talking about the connection pieces, I'm not sure they are available...I salvaged mine as best I could and reused them. Haven't had any problems yet, and I did the fix about a year ago.

Once you reinstall the new harness...verify that the connections are correct. After that, assess what still appears to be problematic, THEN go ahead and decide to replace the offending sensors.

The oil pressure sensor runs about $70. FastLane does have this.

I didn't have to replace my oil level sensor, so I don't know the cost. But FastLane should have that too.

Contact Phil at the FastLane number on this site. If you can't find it, Phil will get you set up.

But as I said earlier, let's get the wires back in shape first.

G-Benz you've been most helpful! Thank you so much for your advice! I'll keep you posted and will post results shortly.

The 93-95 cars had a problem with the Lucas engine wiring harness, althougt MB denies it. The harness was supposed to be enviromentally friendly with the insulatoin breaking up after 30 or so years, but it happens after about 10 years. Eventually the car will stop runing if it is not changed. Mine did ater I changed the plugs. There is a good article with pictures on the DIY page. You can also do a search, there should be lots of info.

Sorry I did not read all of G-Benz's good advice. Sound like you have a different problem tha the main wiring harness.

Sorry I did not read all of G-Benz's good advice. Sound like you have a different problem tha the main wiring harness.

But good point! ;)

Make sure the main harness has been changed at some point. If the other harness looks the way it does, the main one would too.

I had my main harness replaced three years before I saw the second one deteriorate in the same manner...and BOY did it run like crap prior to the harness fix...

Yes! The main wire harness was replaced (as a service record by an authorized Mercedes dealer, as shown in the history of vehicle) before I purchased the vehicle, I believe this was done in 1995. Does this new harness last longer than the original? Will I have issues or should I look out for problems with this replacement harness after 9 years of it being installed?

The replacement harness has the regular insulation that is not prone to "calculated deterioration" as the original. You should be okay.

And yes, MB did originally experiment with using components that would be more suitable for recycling after a predetermined salvage life. The harness insulation was one of them.

Unfortunately, the breakdown was premature, leaving owners and techs alike scratching their heads over the myriad of problems that resulted.

Only the insulation deteriorated...the outer jacket was left intact...so visually, nothing seemed amiss...until someone decided to cut away the outer jacket and inspect...:eek:

New harness problem?
 

O.K. I took all day Saturday off to end up MAKING the 3 wire harness in question. Thanks G-Benz! I did as you said: Completely removed the old wires, took it inside and measured off same length wiring of the same colors and made new wiring, and soldered the original connectors onto the new wiring, and then reinstalled the whole thing....just before I gave it a try, I double checked everything and made sure each wire went to it's appropriate location......EXCEPT now the oil pressure gauge is pegged at the "3" position (just like in the case with G-Benz) and the low oil indicator light is "ON" permanently.....what could have gone wrong? As a reminder, the pressure gauge and indicator lights were working properly before I attempted to change the harness...could these sensors have been damaged when the stripped wires touched? or when replacing the wires? Any ideas appreciated! Thanks!
Andrew Montoya

Re: New harness problem?
 

IN a word...YES. Your sensors are now fried.

My oil press. gauge worked fine until I did the wires...failed after I reinstalled everything. So your story sounds a lot like mine...except I bolted the solenoid wire onto the wrong terminal the first time and couldn't start the car...

If your pressure gauge is pegged at "3" you need a new sender. About $70 at FastLane (at the top of the page). It's a 15-minute replacement job (and you already know how to get down there)...all you need is the proper size wrench...hopefully a short one as there isn't much room to twist...

Low oil indicator is probably shot too. I never did the R&R on that so I can't say if you need to drain the oil pan to replace it or not...