To be clear, my 4-pin description came from the 83-85 ETM section of the W126 FSM on CD which shows 4 pins in use in the glow relay, besides the 5 pins to the glow plugs and big wire from the battery. OP indicates an 83 300SD. I cannot comment on relevance beyond that.

What I would do is disconnect the 4-pin connector and test that +12V comes through pin 1 when the key is in run (preglow) and +12V comes through pin 2 when the key is in start. If your car passes those tests, I'll agree it's a bad relay or wrong relay.

Sixto
87 300D

You did, in fact, purchase the afterglow relay. This relay has no input for coolant temperature and will keep the plugs on for approximately three minutes...........with some slight variation due to ambient temperature.

What you actually wanted was the original, OE glowplug relay that shuts off immediately upon release of the key............the relay that 90% of us are currently using for the 617.

Sixto, I just performed the test you outlined. I get 12+v on pin number one when key in run position. 0 volt on pin 2. I turn key to start while watching the meter and pin 2 gets 12+v until key is released. I also tried turning key to run and not starting it. I did find that the relay turned off in about 30 seconds if key is not turned to start. I like that. If I block the 12+v from the start/violet wire, will the relay always turn off in about 30 seconds?

Before I start cutting into the system, I'm going to start by installing a nice ground strap and see how the charging system keeps up. That may possibly provide enough charge to not worry about the plugs glowing for three minutes... hopefully. If not, I think I may install a small push button over-ride on the dash that can either be depressed(no volts sent down pin 2) or not depressed so the glow relay system operates normally. If that idea sounds bad for any reason do let me know.

I understand some of you are saying I have a faulty relay. But when I look up the part, the description says that the relay will run for up to 3 minutes after start to help smooth things out until warm. This is a new "upgrade" to the part that seems to not be an option. Am I wrong? The fact that my relay stays on for three minutes, like the part description says it will, indicates the relay is functioning correctly... right? I'm just trying to get it clear as to how my new relay is expected to perform.

Thanks for the help!

In my quest to find a relay that functions as OEM I could only find the new version. Where can one find the OE without going to a junkyard?

Thanks Brian!

It's the afterglow relay. You may be correct in that the dealer considers the new part to be an "upgrade" and won't offer the original anymore. That would be unfortunate.

The relay that you purchased is performing correctly as designed for afterglow. However, you'd be much better off with the original relay if it's available.

The old version is available in aftermarket. Call Phil at Fastlane and explain to him what you need...........I'm sure he can get it.

It does appear that Bosch has superseded the old version.

I see. This is all becoming much clearer now. Yes, Bosch is the only brand my local distributor carried. So, afterglow I have. And yes I think you are right Brian, I would be much better off without that feature installed on this car.

Thanks Sixto for the wiring info, very valuable! It's nice to know what the relay is doing with these volt signals. For the moment I think I'll block the 12+v signal from the key start position until I get my hands on an OE relay. I have already installed a volt meter on my lower dash, I hate to keep cluttering up this beautiful interior with unnecessary buttons and gizmo's and meters. No push button for me!

I'll install the ground strap and post back my results. I'm hoping I get at least a little bump in charge current. If I do, I'd think that little bit of info should be broadcast throughout the forum as a must do upgrade!

Thank you everyone!

CD

After reading this entire thread, it seems to me that the real problem is your charging system, not the gp relay.

It is true that there is a fairly large current draw when the glow plugs are first energized, but by design the current draw is greatly reduced when the glow plugs reach their operating temp.

I would agree that cleaning/replacing ground cables would be a good start. You might also check the alternator terminals, a loose or corroded connection could cause problems. What about belt tension?

I would also suggest checking the output directly at the alternator output terminal and comparing with the reading across the battery terminals, you might have a voltage drop there.

Thanks King! When I add the ground strap I'll check the voltage at the alternator. Belts are brand new and tightened to spec. Pulley does not slip. Checked it with a wrench.

Update!
 

Thought I'd give this an update for those of you who participated and followed along. First of all, thank you all for the great advice and info!

So, I grounded the battery from the negative post directly to the engine in different spots. My charging voltage never change/improved with or without the new ground strap. I still get tops 13.2 volts even with the engine reved up. I've had this alternator for about 9 months now and it has always performed this way(just like the two before it). So I'm concluding that I have had the misfortune to have three alternators with lower than OEM output. OR there is just something about my wiring harness that I can't detect that will never allow more current to pass through to the battery. What is OEM anyway? What SHOULD my voltage be on this car? No biggie I guess. As long as I don't install a high powered radio or run my glows all the time, it does keep the battery charged.

As for the glow relay staying on longer than I want. I decided to just interrupt the violet wire from the ignition switch(so easy to do). Now the plugs come on, car starts beautifully, glow ends about 20 seconds later. That works perfect for me. Maybe I'll need to allow the 12v signal to keep the glow plugs on a little longer in the winter time, but everything runs nice and happy with this setup for now.

Thanks again everyone!