OK I've sighed, kicked and cursed long enough time to come to the pro's. I'm working on a 1980 300SD. We recently purchased this car and I've gone thru and elminated most of the bugs... or so I thought. My wife was driving it and she said it slowely lost power and then died. When she tried to restart it all the lights and buzzers came on, lights, windows, all accessories worked, but the car wouldn't crank. Had it towed back.
When I returned home on the weekend it started up and I moved it around a little bit, shut it off and went to restart it. It turned over for a second and then stopped like someone turned off the switch.

I have jumped the solenoid and the engine turns so I'm looking at the ignition switch itself or the starter relay. So here are my questions.

1) Where is the starter relay located on these cars?

2) On the ignition switch I have the lock cylinder out, the bracket bolt is out, the plug is disconnected, and vacuum lines are off. How does the actual ignition switch come out?

3) This one is going to sound stupid but how do these cars actually turn off? My other deisels have electronic components that shut them down ie fuel pumps or injection pumps. This one seems to be all mechanical all driven off of the engine. So what stops it from runnning?

I'm thinking that somehow the car started shutting down while she was driving it causing the slow power lose.

Any info could help as I'll be back at this thing tomorrow.
Thanks
Mcgyver

 

Ok using Dieselgiant's (I'm liking that site) very informative pictures I managed to get the ignition switch out. I also learned how these vehicles shut down. Very interesting. However I still can not locate the starter relay. The ignition switch checked out good and it has good power supplied to it. So that leaves my fault somewhere between the switch and the starter. Which means either the starter relay or bad wiring.
Anybody have any ideas as to it's location?.........
anybody?...............

 

on the starter

 

No that's the solenoid and it's working fine. I can put 12V to it and the car will start and run no problem. From the wiring diagram it looks like a standard Bosch relay. Pin 85 comes from the ignition switch to energize the coil. Pin 86 goes to the reverse switch so you can't start it in gear and grounds the other side of the coil. Pin 30 has 12V. Pin 87A goes to the A/C compressor I assume to turn it off when trying to start the car. Pin 87 is the start lead which also goes to the glow plug timer unit. The reverse lights come on so I'm assuming the switch is good. The car will start in neutral. We live in a hilly area so I'd like to be able to start it in Park. Then there is also the issue of the 12V going to the glow plug timer I'm sure that does something.

Anyway I've searched numerous sites on the web and can't find anyone that knows where this relay is on a 1980 300SD found it for numerous other models and it's not in those locations. I did find three relays on the outside drivers footwell but none of those are tied to the starter circuit.

I've checked behind and under the glove box in the outside passenger footwell peeked into the inside drivers footwell and haven't found anything.

So anyone that has found a random relay will working on their car please feel free to pipe up as it may be the one I'm looking for.

Thanks in advance

Mcgyver01

 

My reply in not going to help you find the "relay" that you are looking for but there is a netural safety switch down on the transmission that keeps the car from cranking in anything other than park or netural. On my 1980 240D every now and then it won't start in park. I can push the shifter to the right and it will start right up. I'm sure there is an adjustment for that but I've been too lazy to try and fix it (plus it's been really hot and I'm a wimp).

Good luck,
Tony T

 

Ok just an update for anyone that may be following along. I drove the car from OH to NC the other night and it did wonderfully. I found the loss of power issue was a clogged primary fuel filter (didn't know there was two) Damndest thing was you could drive all day around town 45... 50 mph short runs at 60. Try and run for more then 5 miles at highway speeds and it would starve. Let it idle for a minute and you were off and running again. Anyway long story short fuel filter. Fixed most of the electrical issues but still have to start in Neutral still trying to find the eluasive starter interupt relay. Tonkyman the switch your referring to feeds this relay. I'm assuming (probably a bad idea) it's good because it also controls the backup lights and they are working.
Anyway car is running good at the moment found a cracked boot on the rear end so that the next immediate problem. Anybody have any good advice on those. Other then take it to the dealership like the manuel recommends.

Mcgyver

 

diesel giant has a tutorial on replacing the axel shaft boots. dont believe there is a relay, just a lockout switch on the transmission itself but i can check alldata for you monday the 9th and get back to you then.