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300GD startup electrical blues

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AmatoBGSG
Posts: 265

300GD startup electrical blues

Post#1 » Wed Jan 15, 2020 8:14 am

Good Morning All!

After giving this problem the old college try, I think I need to seek outside advise! Feedback/thoughts/wisdom/wise-ass comments, are very appreciated!!!

My 300GD n/a (gasser lovingly converted by the West German Border Patrol in the early 80s) has always been really reliable in terms of starting up. However, last weekend, out of the blue, the engine won't turn over. Before I start, I think the battery is ok: measured 11.7V across the terminals last night (maybe drained a bit b/c I have been fussing with trying to get the engine to turn over for a few days now), lights come on, etc... Here's the scenario:

1. Cycle the glow plugs
2. Turn the ignition all the way over
3. The starter lets out a little whimper, and then nothing
4. I turn the ignition back, pull out the key
5. When I immediately try again to cycle the glow plugs I get a crazy buzzing sound from the glow plug relay (it's vibrating too). The radio also comes on (wtf???)
6. When I turn the ignition all the way over, everything stops (radio, vibration, lights in the dash). It's like someone disconnected the battery!
7. Repeat #5 & 6, ad infinitum

This reminds me of what happened when I put in my transmission. I didn't properly secure the grounding strap to the started motor (which is attached to one of the bell housing bolts) and when I tried to turn the engine over it was like the battery was suddenly disconnected. I've checked what I think are the relevant wires, grounds, too see if anything is obviously cracked, split, frayed. So far nothing stands out as obviously bad.

Also, and I do not think this is related, but my turn signals are dead. No voltage going to them when I try to engage. This happened a few weeks before my startup woes though, and I think is related to me removing and improperly re-hooking up my rear tail lights (possible I fried the flasher?).

OK. Sorry this is so long. If you made it this far, thank you!
1980 300GD BGS

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w123_sedan_guy
Posts: 210
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Re: 300GD startup electrical blues

Post#2 » Wed Jan 15, 2020 10:09 am

I'd be curious to see what your battery reads while your trying to start the engine. I wonder if the voltage drops to near 0. Do you have a battery charger or jump box that you could hook up? It seems like jump boxes are never enough to start an OM617 if the battery is totally dead but adding some more juice during a start attempt might give you a hint as to how your battery is functioning.
- Kyle

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AlanMcR
Posts: 4570

Re: 300GD startup electrical blues

Post#3 » Wed Jan 15, 2020 10:19 am

Review all of the major grounding and +12V connections, including the battery posts. I'll bet one of them is loose or corroded.
...Alan

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Flanker525
Posts: 1133

Re: 300GD startup electrical blues

Post#4 » Wed Jan 15, 2020 10:42 am

Sure sounds like a near dead battery to me. There is also a chance that the starter solenoid is on its way out as well. I would get a fresh/charged battery to try out before anything else.
2015 ML250
1991 350SDL
1982 300GD Cabrio PARTING OUT

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AmatoBGSG
Posts: 265

Re: 300GD startup electrical blues

Post#5 » Wed Jan 15, 2020 5:46 pm

Ughhhh... I'm such a dope. Yes, it was only my battery crapping out on me! Why oh why don't I always check the easiest thing first! It's just that in the past when my battery drained I never heard all the buzzing from the glow relay.

Thanks guys for pointing me towards the obvious! :mrgreen:
1980 300GD BGS

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AmatoBGSG
Posts: 265

Re: 300GD startup electrical blues

Post#6 » Fri Jan 17, 2020 4:49 pm

Ok... I started the self flagellation too quickly!

The way the electrical system just died when I cranked the ignition made it seem like a faulty battery wasn't my only issue. I hooked up a multimeter in series with the battery (positive terminal, multimeter, battery cable) and read about 12 V, with everything off. I pulled all the fuses, still 12 V. Then I disconnected the glow plug relay, and the voltage went to zero.

So there's a short somewhere downwind of the glow relay, or the relay itself is crapping out on me. Resistance between the various pins on the relay and the cable from the battery seemed fine. The wiring to the glow plugs is good, and I think the wiring to the ignition is cool too.

Since this is a diesel swap, the wiring setup just doesn't quite follow any diagrams or stuff I can find online. Turns out there is a wire coming from the relay that goes to both the startup valve solenoid, and the 4-pin flasher relay (see picture, I think that's what I'm looking at).

UNADJUSTEDNONRAW_thumb_20cf.jpg


When I unplug this flasher relay (if that's what I'm looking at), then the startup sequence is normal, and the glow relay doesn't buzz and vibrate like crazy if I try to cycle the glow plugs a second time. So I think the problem may be related to the fact that my turn signals aren't working! Wow! What a fun easter egg hunt!!
1980 300GD BGS

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AlanMcR
Posts: 4570

Re: 300GD startup electrical blues

Post#7 » Fri Jan 17, 2020 5:16 pm

If I understand your multimeter hookup, it should show a 12v reading even with much less than a 1mA draw. Such a draw would be less than the battery's internal self drain. Nothing to worry about if it is that low. Even 10mA would be OK, unless you plan on leaving it for months without a battery tender.

To get a proper sense of the drain you would need a milli-amp meter set up in that configuration. Note that the moment that you start using any electrical power you will blow the fuse in the meter. So have a bunch of fuses on hand.

The relay in the picture is an ordinary relay, quite possibly the horn relay. Though it looks like an add-on.
...Alan

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AmatoBGSG
Posts: 265

Re: 300GD startup electrical blues

Post#8 » Mon Feb 10, 2020 3:28 am

AlanMcR wrote:If I understand your multimeter hookup, it should show a 12v reading even with much less than a 1mA draw. Such a draw would be less than the battery's internal self drain. Nothing to worry about if it is that low. Even 10mA would be OK, unless you plan on leaving it for months without a battery tender.

To get a proper sense of the drain you would need a milli-amp meter set up in that configuration. Note that the moment that you start using any electrical power you will blow the fuse in the meter. So have a bunch of fuses on hand.

The relay in the picture is an ordinary relay, quite possibly the horn relay. Though it looks like an add-on.


Thanks for the help... Again!

So yes, I checked the amp draw on my battery, blew the multimeter fuses, replaced them... And it turns out the crapy radio the PO had installed was shorted out/draining the battery.
1980 300GD BGS

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AmatoBGSG
Posts: 265

Re: 300GD startup electrical blues

Post#9 » Mon Feb 10, 2020 3:32 am

In case someone has a similar issue... Indeed my lousy old battery was on its last legs. I still can't figure out why the heck a dying/dead battery would cause the glow relay to buzz. But I replaced the battery and it appears as though all is well!

In the post I mentioned that my turn signals crapped out on me at the same time (lights not turning on at all, but dash indicator staying lit). Turns out my flasher relay died at the same time, which is located next to the fuses. $9 for new relay from Napa (EP26) and I'm back on the road!
1980 300GD BGS

blueg
Posts: 2013

Re: 300GD startup electrical blues

Post#10 » Tue Feb 11, 2020 1:49 pm

Might be prudent to test the glow plug contacts with everything shut off.
Sometimes the relay will stick inside leaving the glow plugs activated until the battery is dead.
Just to be sure.

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