1983 300SD Electrical Problems - When Starting - PeachParts Mercedes-Benz Forum

eatont9999 · #1 11-07-2014, 01:17 PM

Hello,

I have been scratching my head over this problem for the last three years I have owned this car. The electrical problems seem to occur during starting for the most part. Sometimes when driving, the climate control will change the blower/heat and the windshield wipers will come on. Otherwise, the problem exists when starting the car cold or warm.

I get, 9/10 times, one or a combination of the following symptoms when starting the car.

1. Wipers come on and I have to toggle them off - sometimes they do not park under the cowl completely. Sometimes they go for 3 swipes and stop on their own. It is random what I will get.

2. The radio will not turn on even though it has power. The antenna goes up while waiting for the glow plugs and the radio works until I start the car. When cranking, the radio shuts off but the time is displayed on the faceplate. Pressing the on and off button does not do anything. If I wait 10 minutes or shut the car off and try again, the radio usually starts working again.

3. After starting the car, I have noticed that the climate control no longer functions. It usually comes back in 10-15 minutes or if I restart the car but not always. None of the settings turn the blower on - not even defrost and full speed fan.

The problems I am having scream ground issue to me and I have researched the ground connections, checked and cleaned any that looked corroded. I did this for the two grounds near the headlights and the bushel of grounds behind the dash cluster. No change. I inspected the ground cable going from the starter motor to the frame and it is tight with no corrosion visible outside. I have not removed it yet. I also cleaned the ground cable under the battery when I replaced the battery about 2 1/2 years ago. I have not found any chewn or broken wires on the car, so I don't expect any animals have been in there.

The car starts quickly and the glow plugs seem to do their job well. The GPs were replaced about 3 years ago. I do notice that after the GP light goes out, the wipers will occasionally turn on; this happens before I engage the starter. 9/10, engaging the starter before or after glowing, the above issues will manifest themselves immediately.

Someone please help me see what I am missing or doing wrong. Is there anything I can do to troubleshoot the issue more or at least change the symptoms?

funola · #2 11-07-2014, 02:22 PM

Wow, did this happen on Halloween too? It's haunted and needs exorcism. Fun fun fun!

Have you studied the elec diagrams?

LNGfish · #3 11-07-2014, 02:31 PM

My Main Ignition Switch caused various problems with AC controls. Once replaced problems went away.

jay_bob · #4 11-07-2014, 02:51 PM

I agree, sounds like problems in the main switch.

The electrical portion can be replaced without dropping the whole lock assembly.

Be careful, disconnect the battery first, you have direct unfused battery power feeding the switch.

jay_bob · #5 11-07-2014, 02:51 PM

I agree, sounds like problems in the main switch.

The electrical portion can be replaced without dropping the whole lock assembly.

Be careful, disconnect the battery first, you have direct unfused battery power feeding the switch.

ROLLGUY · #6 11-07-2014, 02:59 PM

It may be the combination switch that is bad. Here is an easy test you can do if you have another known good combination switch (turn signal switch) available. Remove the knee panel and unplug the connector that is going to the combination switch. Plug in the connector from your known good switch and try your normal routine. If it does the same thing, you know your combo switch is good. I have a spare complete steering column, and have used it for testing the combo switch in a car. I would have a hard time believing that your problem was the ignition switch, as it only provides the power for the accessories. If they are turned off, they can't get power from anywhere else (not sure if that makes sense). A bad combo switch would explain the wiper issue, but the radio issue is a mystery. If the combo switch turns out to be good, I would lean towards a ground issue. Although you have checked the grounds, that is the problem most of the time with the weird things electrically that your car is having.

eatont9999 · #7 11-07-2014, 03:43 PM

All good suggestions. I'm glad I asked.

I have looked at some wiring diagrams but my ability to read and understand some of the technical items is limited. I replaced the combination switch 3 years ago with a used one. When I bought the car, the turn signals were inop and I diagnosed that to be the stalk switch. That doesn't eliminate the possibility that the used stalk is bad. I have a spare of unknown condition I can plug in for testing.

The ignition switch is something I have not looked into. I have some spare key, lock and switch assemblies from gas W126 cars. I wonder if one of those would plug into the harness on the 300SD for testing.

I was also thinking about taking a jumper cable and connecting it the negative battery terminal and somewhere on the engine to act as another path to ground. If my issues magically disappear, then I will know it is ground related. I might try this first before pulling electrical wires.

eatont9999 · #8 11-07-2014, 03:47 PM

I should also add that to me, it seems like there is a surge of electricity coming from ground when the car is started and it stops some items from working until the charge goes down. Almost like a capacitor. I don't believe it is a lack of power getting to the CC and radio but more like too much power coming from ground. It is hard to explain and I can't prove that theory right now but it seems like something close to it.

eatont9999 · #9 11-07-2014, 05:09 PM

Looks like the switches are the same part number. Now I have two somewhere in the garage to test with.

jay_bob · #10 11-07-2014, 05:12 PM

If your switch is bad then you can end up with all kinds of weird problems. There are multiple switched circuits that come on in position II and you could have a situation where the circuits get crossed due to internal damage in the switch.

The other thing I would try is pull out your fuse tray and make sure nothing is shorting things out on the back side. Make sure it is dry (no water leaking in).

Junkman · #11 11-07-2014, 09:18 PM

I had a radio that would work intermittently. It eventually quit and I stopped by an old school electronics repair place. The owner asked "how old are the speakers?". He said that was the problem when I said the car was an 84 and the speakers were original.

As/s /ming he's right, you have at least 2 unrelated things going on. New speakers are inexpensive. They sound better too.

Crutchfield has some that will fit the front after you make an mounting ring. Get the part number & find them for less elsewhere. Rears can be slightly larger.

LNGfish · #12 11-10-2014, 07:00 AM

Prior to changing my ignition switch I was loosing power to my climate control off and on. I replaced the steering lock while I was at it. It can be done with the steering wheel in place. I think I wrote up some on it here. My car is a 1982 300SD with 160K on it and the contacts were very tiny and were burned pretty bad. Since then, 2 years, no problems. My steering lock was acting up too. so I killed 2 birds with one stone. I got a tumbler to match VIN at dealer and a new key. Ignition switches fail on all cars cause there is allot of current.

oldsinner111 · #13 11-10-2014, 07:05 AM

I changed my ignition switch too.I also on every car I've owned add a extra ground wire,from battery to engine,and from engine to body.These old cars,don't conduct electricity well,like when new.

eatont9999 · #14 11-10-2014, 10:37 PM

Looks like I got a few more suggestions here to try.

I have a little update on some troubleshooting. I tested an unknown condition ignition switch and the symptoms did not change. Removing the fuse for the blower system #13, I believe, allowed the car to start without the wipers coming on. I tested this about 6 times. Oddly, though, the radio seems to have power when the car is off and the key removed. No tunes or front display but the antenna is up and operable with the switch. The "Stereo" light looks dimly illuminated. Removing the fuse for the radio lets the antenna go down but it come up when the fuse is reinstalled.

Adding some jumper cables in various places on the engine going to the negative terminal on the battery did noting at all to change the symptoms.

I am not confident that the ignition switch I tested was any better than the one in the car. It may have less wear but it did not seem to be in mint condition. I noticed that the key had to be turned back a tad after the car started to get accessories to work. Typical issue on these cars. It also came from an SEL, so I did not have the vacuum shutoff. The engine ran for a second or two but that is all I needed for testing the problem.

I am at a few hypothesis right now:

Ignition switch issue.
CC issue - maybe blower relay? I still hear the ducts changing, so CC has some sort of power.
Complete SNAFU somewhere in the wiring I have not found.

Diesel911 · #15 11-11-2014, 11:10 AM

Quote:

Originally Posted by eatont9999

All good suggestions. I'm glad I asked.

I have looked at some wiring diagrams but my ability to read and understand some of the technical items is limited. I replaced the combination switch 3 years ago with a used one. When I bought the car, the turn signals were inop and I diagnosed that to be the stalk switch. That doesn't eliminate the possibility that the used stalk is bad. I have a spare of unknown condition I can plug in for testing.

The ignition switch is something I have not looked into. I have some spare key, lock and switch assemblies from gas W126 cars. I wonder if one of those would plug into the harness on the 300SD for testing.

I was also thinking about taking a jumper cable and connecting it the negative battery terminal and somewhere on the engine to act as another path to ground. If my issues magically disappear, then I will know it is ground related. I might try this first before pulling electrical wires.

I don't know about the Electrical part but the pics of gasser Steering Colum Locks I have see they do not have a place for the Vacuum Shutoff Switch that mounts on the Steering Colum Lock.
You will know by looking at the one your have.

If it does have the big hole and the 2 threaded holes for the Vacuum Shutoff Switch look inside ot see if it has the Plastic Cam that operates the Vacuum Switch.