I have read on lot on the forums and done a lot of work and am still stuck. I may just be having bad luck but if there is any test I can do before I start buying and replacing I am hoping I can find it here.

The problem is intermittent starting. It either starts up perfectly and quickly. Or the solenoid clicks loudly but the starter does not turn at all. Battery has been tested and swapped. Starter has been replaced. Wiring has been tested.

All I can figure is that the solenoid contacts are not making a good connection...sometimes. Very frustration because it will usually work fine. But then it doesn't and you are stuck. It happens with the engine hot or cold. With the ambient temperature in the teens or in the eighties.

Short of replacing the battery, starter (again) and all wiring what can I do to actually figure out what is going on?

I had a similar issue once, turned out that I had gotten a bad rebuilt starter. Other than that check all the battery leads. They can corrode internally and cause high resistance.

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

Problem could be in your neutral safety switch if it acts up you could try jumping it on your fender well if it starts that eliminates that. See if the starter is getting voltage if so jump it. I ounce had a problem with intermittent starting before I traced all wires and voltage to starter finding that there was a broken small wire at the tip where it connected to starter and it would work and not work. Went thru many starter installs for nothing till I figured this out finally.

How many starters? Were you pissed not doing the easy stuff first?

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Remember, this is a long distance diagnosis so all bets are off as far as guaranteed accuracy......

That said, it sounds like the starter has a bad commutator segment. In the olden days we'd use a gizmo called a growler to check each segment for connectivity as a part of the starter rebuild process. In the days before commercially rebuilt components were commonly available shops like the Buick dealer that I worked for did on-site rebuilds so we could save the customer some money and get them back on the road. If there's an open segment in the commutator (that's the part that rotates) the starter will work fine until it happens to stop with one of the brushes sitting on that bad segment then no connectivity = no rotate.

EDIT: If the neutral safety switch was bad there would be no solenoid click when you turn the key. The NS switch stops all power from initiating the start process so the solenoid would never try to click. So while a no-start should include a look at the NS switch, if the solenoid clicks, that ain't it.

If you have a decent local rebuilder of such components (we have Coastal Rebuilders here in Wilmington) they can test the commutator and tell you for sure if that's the issue. If not you're sort of stuck with taking the starter back to the store where you got it and trying another one until you find a good one. Other than being stuck with the effort to remove and replace it, that may be your cheapest option.

BTW - I patronize our local shops (Coastal Rebuilders, a local transmission shop, local car audio shop, etc.) as much as I can partly because I get good work and partly because they're a great resource and I want them to be around in the future. I'd suggest that you at least consider the same approach.

Dan

When it clicks and fail to start, jumper the terminal block (big screw to small screw) on passenger wheel well. If it starts every time with the jumper, problem could be anywhere from the ignition switch, NSS, all the connections and wiring in between. I'd start by cleaning all battery terminal cable connections and the ground strap on drivers side from bell housing to frame and see if that helps first.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I recently went through this in my SDL. PO had installed a newly rebuilt starter 2 days before I took the car home. Worked perfectly every time I used it for the last year, then suddenly started this business where you'd hear the solenoid click, but no starter. Cycle the key a couple times and usually it would pull in and the starter would fire, until one day it stopped clicking, though you could tell it tried to do something because the dome light would dim slightly.

Pulled the starter and opened it up. Whoever did the rebuild had slathered the plunger on the solenoid with axle grease. Big no-no. In time it gummed up and wouldn't let the plunger move. Stripped it out and it's been fine since.

The solenoid has to make full-travel in order to close the contacts for the motor to run. If there's anything in there that prevents it from bottoming out, the contacts aren't gonna close and the motor isn't gonna spin.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

Definitely not the NSW. That was my first thought because that has always been the problem before. I replaced it with a new Mercedes switch and thought I had it fixed for a week or two. That is how random this problem is.

I just disconnected all the wires. Everything looked fine. Old but no obvious issues. There is just the smallest amount of corrosion on the starter end of the small wire that activates the solenoid. See attached photo. I think I will replace this wire with new.

I am skeptical of this being the problem though. The solenoid never fails to make a strong clunk sound. Could lowered voltage due to resistance through this wire be enough to keep it from engaging the contacts firmly enough. Should I increase the wire gauge? Does this wire get power directly from ignition switch. I could add a relay on the fender in order to feed more amperage to the solenoid?

Pretty sure the problem is not before the connections on the fender because it happens no matter wether I use the key or remote starter straight from the battery.

Attached Thumbnails

 

check engine ground,or add another.I always add extra grounds to my vehicles.They charge better.

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

That makes sense. This problem started on what I believe was the original starter and then again on a good used starter. Did not go more than a few days without starting again so it makes me suspect something outside of the starting cause the lack of contact.

Just trying to elimate every other possibility before I remove the starter again.

It never has a problem cranking and I checked ohms between negative battery terminal and block. Where would you add a ground (location on engine)?

I feel like a ghost hunter here or something. I hooked up voltmeter between lugs on solenoid and fed power straight to trigger lug from battery with remote start cables and every time I press the button the voltmeter ohms zero out immediately.

Really hard to diagnose when the problem hides for days at a time...

When it clicks but not spin the engine, did you try banging on the starter with a big iron pipe or equivalent? If that gets it spinning, that could indicate worn brushes or cracked solenoid housing plastic where the terminal stud/nuts are. Some people over tighten the nuts, cracking the plastic resulting in the copper shorting bar not make good contact anymore. Those nuts make an electrical connection, not mechanical. Make them just tight enough so the nuts do not come loose.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Ditto on check engine ground. Once when I had the cluster pulled out in my 1985 300D, I actuated the starter (forgot why) and noticed the speedometer cable smoking. That clued me to sand the connections on the ground strap from transmission to body, then coat w/ silicone grease. There is also a ground strap from BATT- to the frame. If it is a voltage loss issue, you could find where using a multimeter while trying to crank. All the starter cares about is the voltage from its case to the big stud +12 V feed. If >8 V while cranking, a good starter should work. You could have excessive drop on either side. The solenoid is integral to the starter (unlike 60's Ford), though I think can be unbolted.

__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

I am going to clean the engine ground strap just for the heck of it but I think that the problem is internal to the solenoid. I took all the wiring to the starter out and looked over it. Everything looked good and I made a new trigger wire from the fender to the small connection on the solenoid. Cleaned everything really well put it back together with dielectric grease and it started right up. Drove it 50 feet turned it off, tried to restart it and just a clunk.

One trick seems to work. If I connect my remote started button at the fender and press it in rapid succession it will catch and sometimes I can even hear what sound like a little electrical sizzle right before it goes. After that I can start it right up with the key

Would a bad ground cause this?

Is it possible that the voltage from the key is too low?

Could I add a relay to get more juice to the solenoid?

If I replace the starter with new should I also replace the battery just in case?

Thanks for all the help so far!

Measure voltage and current for the solenoid. Solenoid should draw around 7 to 8 amps. Use the ground at the starter and not at the battery for a true reading the starter is seeing. I am not sure what voltage you should get but my guess around 11 to 12 volts if it just clicks and starter does not spin. If it spins, you'll see lower voltage due to higher current draw, my guess 8 to 10 V. If your key switch contact is marginal, i.e. higher resistance than normal, it will reduce the current drawn of the solenoid. If you measure only 5 amps for example, it could be a bad key switch, or a bad starter ground, or bad wiring in that circuit.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked