A month ago, I had a no-start. No power to the starter, or glow plugs. Nothing happening when the ignition switch was turned. this was 5 minutes after driving it 20 minutes to town for mail and errands. Roll started the car, drove it home, and swapped out the ignition switch..

The Original ignition switch was covered in oil, and I suspected the fuel shutoff has been leaking oil for a while and that was what killed the contacts in the ignition switch...

NOPE!

Now I am getting a faint Alternator idiot light glowing when driving at night. Not instantly at start-up, but it develops within a minute or two. It starts out faint, and the headlights seem to make it worse. Have checked the battery voltage at this point and it is typically charging at 14.35 volts...

Sometimes when I use the brakes the charge indicator light goes to full bright.. and the gauges go wacky.. (again this happens at night or when the headlights are on) I was thinking it was a short in the circuit board of the instrument cluster..

NOPE!

I have also just noticed-recognized that it will on occasion trigger the pre-glow light, and the Glow plugs will cycle on... What the heck?

at present I am starting the car and then un-plugging the glow plugs.

I want to blame the ignition switch for the glow plugs, and the no-crank start experiences..but I am now doubting that the original ignition tumbler was actually faulty.


Of course sometimes the dang thing behaves perfectly.. Although that is becoming a rarity..

Any and all suggestions are welcome, as to where to start on this

__________________
'83 240D
'85 300D
'86 300SDL
'88 300E

Probably a failing neutral safety switch, or missing shift rod bushing(s).
If the NSS is activated/sticking you will get a starter lockout.
This can also (maybe??) cause the glow plug relay to activate randomly.

'Desert Rose' had a recent spate of starting circuit gremlins after being trouble free for years.
Initial symptoms onset about 4 months ago: radio cycling off and on traversing rough roads, occasional activation of starter on shutdown,
no start (or click) turning the ignition key and having to giggle the shift lever when starting the car,
and then the glow plug relay remaining on after starting the car.

Replaced electrical portion of ignition switch (contacts were burned inside the switch).
This cured the radio cycling and the starter activating on shutdown.
Replaced the missing rearmost shift rod bushing, and this cured the need to giggle the shift rod lever on startup.
Replaced the defective glow plug relay with a good used spare.
All starter circuit electrical connections inspected and cleaned.
Starting problems solved for about two months.

This morning the NSS failed, connected a jumper wire to the starter solenoid.
With the ignition switch on, and a brief contact of other end of jumper to positive battery terminal, the car started right up.

Ordering a replacement NSS today.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

I might clean the grounds.

Thanks for the replies: I will revisit the electrical part of the ignition switch. The car is a manual and does not have a NSS any more.

Anyone have thoughts on why-how the headlights appear to make the battery charge indicator light glow faintly. It has to be dark to be seen, it is not bright enough to be seen in the daylight.. UNITL one uses the brake lights..

Which brings me to the topic of checking the grounds.. Is that to look at the grounds behind the instrument cluster, or somewhere else... OR check every ground in the car??

__________________
'83 240D
'85 300D
'86 300SDL
'88 300E

Check all the ground and especially the ones behind the instrument cluster.

Ok Got it. That will be at the top of the list tomorrow AM.

Thank You all for the guidance, and suggestions!

__________________
'83 240D
'85 300D
'86 300SDL
'88 300E

Also check the engine to body ground at the rear of the engine and the battery ground.

Yes, definitely clean all the connections behind the instrument cluster and in the starter circuit (as I had done).
Remember to turn off your radio first and then disconnect the negative battery cable before you start cleaning the connections.
I like to use the DeoxIT-D contact cleaner followed by the DeoxIT-Gold conditioner.

You will want to clean/rejuvenate the battery terminals and clamps, the negative battery cable to chassis connection,
the positive battery cable to starter connection, the starter to alternator harness ring connections, the alternator harness female spade connectors,
the alternator male spade connnectors, the alternator body to chassis ground connection (grounded via the bolts attaching the alternator housing to the alternator bracket),
and both ends of the ground strap between the transmission housing and the chassis (under the exhaust downpipe).

The alternator should have a thin spring steel wire clamp that locks the alternator harness connector to the alternator, if it is missing, the plug can become loose from the engine vibrations.
This can cause inadequate charging and illumination of the instrument cluster warning lamp.

Since the ignition switch is new and there is no NSS, doing the above should hopefully take care of the issues.

__________________
78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Thanks for the replies. They are helpful in keeping my mind open to possibilities. This is my first experience in electrical troubleshooting of a "real" nature, and it can get daunting!!

I went looking for the chassi to engine ground, and found one on the drivers side, between the bell housing bolt right at the bottom of the oil filter canister. NONE seen on the passenger side of the vehicle!

Anyhow I cleaned the one I found, and cleaned the grounds behind the cluster. Changed the cluster with another one I Had in stock....

AND I think it has something to do with the multi-pin connection that goes to the instrument cluster. Is that even possible?? By moving that connecter or the wires attached to it, I can get the Glow-plug relay to come on... For the moment I am out of time, and need to drive the car, lets hope it makes the 100 mile trip today, and returns on Sunday. I will be traveling during DAYLIGHT hours only until I get this figured out.

__________________
'83 240D
'85 300D
'86 300SDL
'88 300E