I have a 1970 220d. Just dropped in a new motor. The ignition turned on, all worked great. I held the gorilla nob out to warm the plugs, and I lost ignition key function.



Lights work. Done light works. Key buzzer when when door is open. But no voltage to cluster, glow plugs, or starter remote.



I'm going through the diagram. Gonna make some lunch and think. But any suggestions on where to start? And is their obviously something wrong with my glow plugs that caused a short/fried something?


Thanks.


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Is the ground strap from the starter mounting bolt to the body installed? Are you sure the key is physically turning to position 2?

If so look at circuit 30. In the 220D it's simple and does not have any fuse. The main junction for circuit 30 is the headlight switch. Since you have headlights circuit 30 is intact to that point.

From there it travels to the ignition switch. From the ignition switch in position 2 it goes to the cluster and the glow plug switch - gorilla knob. I would check for power to the radio in position 1 and see if anything else works in position 2 like the blower and wipers etc. If nothing related to the switch works check for power into and out of the ignition switch at the connector.

Circuit 30 is very robust. If you find a damaged switch or melted wiring be sure to check the glow plug wiring on the new engine. The glow plugs on this model are the loop type and are wired in series. The 220D does not have the strip fuse found in the later W123 cars. If circuit 30 is shorted at the engine the glow indicator would glow very brightly very quickly. However, when the gorilla knob is pulled all the way to start the engine the glow indicator is bypassed. That would create a dead short in an unfused circuit with damage resulting.

__________________
1969 220D 5 Speed (OM616)
1983 240D 4 Speed
1985 300D Auto 376K
1985 300D Auto 275K

Thank you so much! I saw that in the diagram but was confused by it. I'll shoot a pic, but I'm guessing this hot mess with three red wires at headlight switch is 30?

I think that short in the glow plug is exactly what happened. I put the set in from my old motor, jumped the power source on the main fuses from #1 to #2 and got juice everywhere. I got 12V to the plugs after by pulling the knob, but my salt shaker never got hot, so I'm assuming there must be a diode in there.

I'm pulling 30 off right now. I believe if I check conductivity from 30 at headlight switch to source side of #2 fuse with ignition switch turned to #2 I will narrow it down to switch, or wiring in between? Are there any connections between output of switch and fuse Panal I could check?

I'm not too excited about pulling the switch out. Lol.

Oh, and no power to radio at position #1. I'm hoping once I get 30 apart at headlight switch I'll find the culprit.




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I spoke too soon. Someone has ran into this problem before, hence the new plugs on my old motor.

I got it apart and two wires going to were melted off a crappy previous repair. Tested conductivity, success at position two. Jumped hot to two wires direct from battery, turned key, BOOM!

Thanks so much! I am so happy to not have pulled that key.

For the future, get that boshe fast plug system, or at minimum run a new circuit from battery with a relay and fuse, use my original glow plug wire at plugs as the switch?

Install fuses onto circuit 30? After headlight switch? Somewhere after starter?


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I assume by "BOOM" you mean it ran. Great news!

If you want to add a strip fuse I would do what Mercedes did on the early W123 (77-79) and add it to to the glow circuit at the firewall. Get the holder and wire that goes from it to the glow plug at the back of the engine. Connect your original glow plug wire to the other side of the holder and mount it to the firewall. These holders were used in other models too.

Keep in mind that the only reason Mercedes added this fuse was because a glow controller could stick and run the glow plugs continuously causing a fire. That situation is impossible on your car.

I've run and parted many of these cars and yours is the first I've seen with damage to circuit 30. I wouldn't get too worried about re-engineering it. This same type of circuit is used nearly every car and is usually not fused. That said I think the strip fuse at the glow plugs is a good idea.

I've never had any problem with the loop system and the only advantage I see to a pencil type conversion is a shorter glow time. I drive a 220D so I'm not in a hurry! The disadvantage is the loss of the very simple and direct dash indicator. What you see on the dash is happening in your engine.

If the previous repair failed when you tried to start the engine there may still be a problem. If the repair was tack soldered and it melted then the current is still high. The "hot mess" you saw on the light switch is indeed circuit 30 and any repairs made to that circuit must be well made with wire of the same gauge. I'm not a fan of butt splices and after making a good mechanical joint by twisting the wires together I solder and heat shrink the joint.

__________________
1969 220D 5 Speed (OM616)
1983 240D 4 Speed
1985 300D Auto 376K
1985 300D Auto 275K

Awesome. Yes I just did that. I had to clip the source wire a little, drill out the hole in the switch, twisted and soldered. I'm using liquid tape. I had the leftover over alternator wire from the junkyard motor with the perfect ring clamp on it.

I'm glad to hear you haven't seen this problem before. And ur right, I shouldn't be a hurry.

No haven't started yet. I killed my charger, and realized I have the muffler hanging low. I'm fixing that, trying a jump start, but might just push it down a hill to start it.


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Edit: I've discovered the source I believe and posted again below.

Alright, got everything buttoned up. Charger died and couldn't get a good enough connection jump starting to crack the lines and bleed the air out (I'm a redneck, I know)

So I hooked it to the tractor and towed it around. Definitely a lot of air, but got it running. Had a few minor touches and just finished. Onto this switch.

I've got quite the interesting situation. When I hooked up circuit 30 to the switch it heated up quick. I disconnected it and ran without it, since I spliced my ignition wires in above the terminal.

Im chasing shorts, and I have ground to every fuse in the box except #1, which is hot.

#2 and #3 showed less voltage when running the meter backwards. The rest a full 12V.

I don't know how it hasn't caught on fire. Lol.

Before all this I had windshield wipers working. Blinkers work but blinking double speed.

On the wires on light switch (disconnected from switch), I have the following going clockwise from backside of switch, starting at 30:

30: blank (not hooked up)
Pa: 12 volts. 2 green/white wires
N: dead, no N or voltage. 2 grey/green
58: ground. Grey
PaL: blank.
N: ground. Grey/yellow
57: ground. 2 wires. White/yellow and white/green (smaller)
56: blank
PaR: blank

This doesn't match my diagram. I'm wondering if they doubled up stuff. The light switch was hanging beneath the dash.

I'm gonna lift up the fuse box and have a peak. And try and wrap my head around this.

Got any ideas?


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Alright fuses 2-6 were shorted by the cluster. I had previously installed a temp gauge in place of the non working clock, soldered wires in for the light in the temp gauge. Haven't opened it yet prob melted the solder making a mess on the board.

Disconnected the three power source wires from the fuse box, and determined the short on the headlamp side. Very low resistance, but I double checked with a test light hooked to the positive on the battery, and it lit up 100% when touched to the fuse box, all three sets of lights.

I had happened to disconnect one parking light (fuse 7), and when I touched light to fuse box at #6 it was a lot dimmer.

I pulled the left headlight, lol, and it's still shorting. It's late and I felt I might be overlooking something and walked away for the night. But next I'll unhook #10 and #12, high and low beam for left headlight, and test the wires seperate from the fuse box.

Does it sound like I'm loosing my mind? It feels like it, this is so odd. I'll take the battery out and inspect the wire from fuse box to left headlight.

It's odd the fuses didn't blow, but with pulling one parking light off and getting more resistance, I'm guessing I have a slight short on each of these 6 circuits, which added up to enough for circuit 30 at the headlight switch to cause heat.

Is there a common place where these wires will run and wear? Like I might have already been shorting a little and when the glow plugs happened it intensified the problem?

When chasing electrical problems on a W115 a good place to start is with a cleaning of the fuse box terminals and replacement of all the fuses. The location and type of fuse in this model can lead to bad connections or outright failure. You can chase intermittent or inexplicable electrical issues forever. Nothing in the fuse box will solve your circuit 30 problem but it may solve and prevent other electrical problems.

In the W115 all the headlights are fused individually. They get power from circuit 30 at the switch but after that they have their own individual fuse. All the other lighting circuits are fused as well. If headlight wiring were the problem you'd blow the fuse for that wire.

Your circuit 30 problem is somewhere else. The headlight switch isn't the problem either since it only directs circuit 30 power to different lights. It can either not send power to a light or send power to the wrong light. If it was completely shorted out it would just light all the lights. If it was shorted to the case it would only short out when installed - not when it's hanging. If you suspect a shorted case put a test light on it. Other than a solder bridge to the case I highly doubt that too.

The most likely circuit 30 problem is still the glow plugs. It's the only circuit that can draw high current without immediately bursting into flames. Remember the entire current of the battery is available to circuit 30. If a small gauge wire were shorted it would blow a fuse or burn immediately. I would check the switch in the gorilla knob. If someone swapped wires around trying to bypass the switch you may have glow plugs on anytime the key is in position 2. Check the glow indicator wiring too.

If you're worried about the homebrew temp gauge just unplug the cluster while testing circuit 30. As long as the oil gauge line is connected you can run without it.

__________________
1969 220D 5 Speed (OM616)
1983 240D 4 Speed
1985 300D Auto 376K
1985 300D Auto 275K

Edit: here's what I'm doing wrong. Using the test light connected to the negative battery terminal. Multimeter isn't showing resistance. So I'm seeing the circuit 30 being grounded somewhere and feeding it through.



I was thinking about picking up a modern fuse box and replacing that whole thing. If I ever blow one I don't even know where to get a replacement.

Here's some thoughts:

With circuit 30 disconnected from headlight switch, it is fine. No connection to ground what so ever.

With power disconnected from fuse box, the headlight circuit is showing about 2.5 ohms resistance to ground. When I disconnect the wire from the fuse box going to headlight, I get 5 ohms to ground on each of the wires leading to headlights.

Cluster was pulling 15 ohms to ground, so it worked fine but I would find myself with a dead battery eventually.

57 on the switch is a ground, I need to measure resistance to circuit 30 and see if my switch is bad.

I'm gonna go double check on this after a good nights sleep, and probably replace my box. As well, test every circuit individually. I noticed on my headlight switch (when hooked up without 30) that I got conductivity between 30 and all 3 power wires at position 1. I should have only got running lights and tail lights, which leads me to believe the fuse box is connecting everything.

But as your suggestion I'll start at glow plugs again. With circuit 30 disconnected from light switch, glow plug operation was normal. No voltage with gorilla knob in stop or run position, full voltage with it pulled out and starting. I glowed for a whole min before starting and no heat to circuit 30. But I didn't check glow plug resistance to ground, which I should have done at the very start before this happened, so we can conclude that it takes me 3 times to learn. Lol.

I can't thank you enough. Without your help I would be towing it in.


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Will these fuses say the amp rating on them? Or does anyone have a list? My FSM doesn't tell me.


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Ok. Thanks. Despite seeing conductivity through the right headlight circuit, I think you are right about glow plug circuit. I jumped power before the fuse to lights, all worked, no heat, no blown fuses. Either my meter or I am crazy.

With battery disconnected, I measured resistance from negative post to first glow plug. Full conductivity when gorilla switch is pulled to glow and start.

So I need to start disconnecting the glow circuit. Salt shaker isn't working so I'm wondering if that's it. Easy fix, despite being kinda cool I don't need necessarily need it. I'm on the coast in California and don't even need glow plugs.

Edit:

I must have power feeding through a common ground. So I'm getting conductivity fed back through but the lights won't pull juice.


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Last update:

I've got it all hooked back up. The terminal for circuit 30 heats up when I run the lights. The head lights work in position 1 and not 2. Tail lights and running lights work in both positions.

First glow plug gets 12v. Second gets none. No heat to circuit 30 when glowing.

Jumping directly to the glow plug gets same results.

When I'm glowing I get high resistance to the plug. When I'm starting I get no higher resistance.

It's like I'm not getting enough current through the gorilla switch.

But, I'm at the point when I'm burning time with not enough experience. I saved a ton by putting this motor in myself. I've learned my lesson to test my glow plugs before using.

I think I'm calling it and taking it to an expert.


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Any old timers see the OP's name....and ' electrical problems' in the title and think .... of course he has electrical problems !!! ?

Edit... several English makes from a long time ago used ' Lucas ' electrical systems.... MGB, Jaguar .... they were notorious for having electrical problems...

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Haha. I just learned about this.

I'm going through the FSM currently. Realizing I have full voltage at terminals 19 and 17 out of the knob, so my resistance control is not functioning in the knob. My salt shaker isn't working. I'm reading full voltage at the glow plugs when pulling the knob. But not getting any currant. I believe.

More to read and test. I'm giving my self the rest of today. Then it's going in.


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