The plugs are normally glowing while cranking. (If that were not the case, these engines would not start in cold conditions. Anyone who doesn't believe that is invited to attempt a cold weather start immediately after the relay times out.) I suspect that disconnecting the purple wire will prevent the timer from going into the afterglow mode, meaning that the relay will open much sooner than the three minute afterglow period.

I have the Bosch afterglow relay in my '82 300D. If there is no start attempt, the relay opens in under a minute. Disconecting the purple wire should prevent the timer from "knowing" that a start attempt occurred.

While I agree with the glow while cranking, many times the 603 would exhaust its full glow cycle in colder ambients and immediately start upon turning the key.

The glow plugs do not need to be energized to effect a start.......however, some heat is required in the prechamber area.

With regard to the OP, it's agreed that he has procured the wrong relay for that vehicle and must return it for the OEM product.

You are attempting to apply 60x theory to an aftermarket 617 part. The later models had the temp sensor in the timer. It used ambient air temp, not engine temp, to determine the duration of the preglow lamp illumination. The Bosch afterglow relay in question has no provision for monitoring engine temp.

How did you come to that conclusion? The Bosch afterglow relay is specified for both the 616 and 617 engines. (It is packaged with 4 glow plugs!!!) I have one in my '82 300D and am quite happy with it. And a number of other forum participants have reported the same. No way is it the wrong part. It might, however, not be a good choice for someone who makes extremely short trips. But, neither would a diesel be a good choice.

I consider it the wrong part for him...........and, I'm also curious as to why any of you fellows need it in warmer ambients? This one has no issues until it gets quite cold.

I've owned my car for about 5 years now and the most annoying part of the charging system is that when everything is tested and known to be good I've never gotten more than about 13.2v from it. I would feel so much better with about 14.1v... 15.5v seems a little high, did you have to tweek your voltage regulator to get that much? Never the less, I think I will try adding a direct ground to see if I get a charging jump.

Thanks for the idea!

Turn on the headlights and the blower and as many interior lights as you can.

Start the engine and run it up to at least 1500 rpm and hold it there.

Now check the voltage...........see if you get close to 14V.

The part I bought is in fact the Bosch kit that comes with 4 plugs, and then you buy an extra plug to complete the kit. It is listed for my car on all the best and well know parts sites and is considered an "upgrade" from OEM. Now, I'm no expert on how the relay is supposed to act when the key is turned and all that. All I know is that after I start my car, no matter the temp outside or if I just shut it down and re-start, the plugs will glow for three minutes.

I just checked the relay and it does in fact have only 4 pins on the small connector. So if that means it is not an "afterglow" model, then what does it mean that it does not shut off for three minutes?

I've always known diesels are a poor choice for short distance driving. I used to drive much further every day and I still do plenty of 1500+ mile road trips... YOU CAN'T TAKE MY DIESEL MB FROM ME!!! :)

So is my system working correctly? I just am not supposed to drive such short distances?

Correct. The glow plug system is strongly suggesting that you consider the use of a bicycle.;)

I get 15.5 with glow on,lights,sub and amp,defrost high,it drops too 14 in a few minutes.Add that extra ground,everyone will be happy.
Now a stuck regulator will put out 16 all the time,burnt battery out,lights.
Easy way to check a weak battery,get voltage meter. Touch negative and positive on battery.Have someone start car,if it drops below 10 volts,battery is toast.

So I got my hands on a shinny new digital multimeter so I could get very accurate volt readings to you guys :)

Battery freshly charged from a long drive. Key off I have 12.81 volts. Key on and glows going strong battery drops to 12.32 volts. I start up and the voltage stays about the same. 12.25-12.32 volts, even when I rev it up. I turn all loads on(lights, blower, radio, door open) and my volts drop to 12.13 reved. This is on a freshly charged battery that holds 1100 amp load for 10 seconds no problem. Three minutes running and my glow relay turns off and my voltage jumps up to 13.11 volts reved(12.95 idle, battery still recovering I think). I will drive it for a while then check the charging volts before shutting it down to see what I get on a nicely charged battery.

So as you can see with my loads on test, during my glow cycle, there is not enough juice to maintain my battery. Drive short runs a number of times and thats it, no start is imminent.

I've replaced my alternator three times trying to get more charge current but 13.11 is the best I can get out of any alternator I've ever put on the girl. Do I need to look into the grounding? Or is 13.11 typical for this 83 300sd? Or do I just need to start taking the long way to work ;)

Grounding jumped my charge 1 whole volt.

I think I'll be trying out the grounding idea... my neighborhood is not very bicycle friendly. I'm not sure I'd survive the ride :eek:

It means that certain members are providing you with information that is totally relevant to a vehicle model that you don't have.

Ok, so I have a small connector in my relay which has 4 pins. That means I don't have an "afterglow" relay. I'll take that as a fact. No temperature signal coming from the engine will provide my relay with any information. Got it. I am going to try to get my charging system to pump out another volt but, I think I would also like to, dare I say, rig the relay to function differently from it's manufactured purpose. I want it to shut off the moment after I start my car. Again, I live in Dallas TX. Glowing the plugs for three minutes after start in even the most inclement weather here, in my opinion, is not necessary. In fact, before I replaced my relay, on warm mornings with a engine that cooled over night, it would start right up without any glow. Once the temp gets down in the high 70's, it starts to take a lot more effort to start.

I'm willing to install a toggle or button or cut wires at this point. Just need my system to charge right after starting.