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Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53901
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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1987 Mercedes 300sdl: neutral safety switch..driveway..mechanicaL

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1987 Mercedes 300 SDL: The neutral safety switch appears to have frozen due to the cold (I left the car in drive for a day and a half in the driveway.). Questions: where is the switch located? Is it mechanicaL, and if so can it freeze in the "off/safety" position? Can I bypass the switch by connecting the positive battery to the positive on the starter? If so, where is the starter motor located?

HiCustomer I can answer all of those questions for you but first can you tell me why you think it's a neutral safety switch problem? What are the symptoms?

 

Marty

Customer: replied 8 years ago.
Marty: Car ran fine on Saturday. I inadvertantly left it in drive when I parked it in the driveway upon returning. This morning when I tried to start it (as said, all panel lights work, glow plug preheat light and buzzer works, battery is fine), I got nothing. No click, no sound, nothing. Noticed it was in gear. Shifted to park and tried again. Nothing. Shifted various times and still nothing. The coincidence of it being left in gear, severe cold and exactly the reaction (non-reaction) that I would expect from trying to start it in gear leads me to guess that the problem is the cutoff switch.
Customer: replied 8 years ago.
Marty: I think I have replied. Here is what I said:
Marty: Car ran fine on Saturday. I inadvertantly left it in drive when I parked it in the driveway upon returning. This morning when I tried to start it (as said, all panel lights work, glow plug preheat light and buzzer works, battery is fine), I got nothing. No click, no sound, nothing. Noticed it was in gear. Shifted to park and tried again. Nothing. Shifted various times and still nothing. The coincidence of it being left in gear, severe cold and exactly the reaction (non-reaction) that I would expect from trying to start it in gear leads me to guess that the problem is the cutoff switch.

Ok Tim, it's a mechanical switch on the driver's side of the transmission. If you swipe the shifter back and forth a few times and try starting it in neutral you might get lucky. As long as the linkage is still attached there is a plastic driver that may have broken on the switch itself. We can hot wire the starter directly from under the hood or we can do some testing at the neutral safety switch. We probably should start with the starter. You'll need a test light or a jumper wire. The starter is located at the lower right rear of the engine. Take a look and see if you can access the solenoid easily enough.

 

Marty

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Customer: replied 8 years ago.
Marty:
I think you have helped and will happily accept to insure you get paid. In looking under the car, I notice what appears to be a cable with a slotted end piece hanging loose from the underside of the car. It is midway from the front, comes ouit of a tube, and is located just to the left of the exhaust pipe, right above what I believe is the catalytic converter (a unit roughly rectangular, in the exhaust system, forward of the muffler). Could this be a mechanical connection to the cutoff switch? If so, any thoughts on how I reconnect it?
If this is too complicated, I'm going to try looking for the solenoid on the starter and just try connecting a cable from the battery positive to the positive on the solenoid, with the ignition switch in 'run' position.

Tim

Tim

Hi Tim, there's no connector on the harness underneath the car. It's just straight to the switch on the driver's side of the transmission. You can jump the starter from the big cable on the starter to the little wire on the starter. Leave the key off so it doesn't start yet. You just want to make sure it works right now. If it works let me know and I'll help you further with the diagnosis.

 

Marty

Customer: replied 8 years ago.
You're a good man, Marty. Going outside to try it now. Already tried connecting the battery positive to the positive on the starter. Got a whirring, but it didn't engage the engine itself. Now going out to try your approach.
IN the meantime, describe where the transmission is? I know, how stupid can he be. I'm assuming directly rear of the engine, but I'm going to have to jack this car up to go looking for the switch. So why not ask first to insure I'm jacking it up from the right corner. Left front?

Tim

Tim

No problem Tim, you'll want to jack up the left side of the car behind the front wheel. Make sure you use a jack stand! The neutral safety switch is just above the transmission pan about halfway back. It would be about in line with where your right knee would rest in the car, directly below at the center.

Customer: replied 8 years ago.
Marty:
You continue to impress me. When I'm done, win or lose, tell me how to switch my deposit to the 'expert opinion' level and I'll be happy to do it.
In the meantime, I tried connecting the positive of the solenoid (the one with the large cable directly from the battery positive) to the negative of the solenoid (the connection that has a much smaller wire connected to it). I got nothing whatsoever. Yet I don't think the starter is dead, because when I connected (earlier) the positive of the battery to the positive of the solenoid directly, I got an audibly obvious whirring. But it was clear the starter was just spinning. It wasn't turning the engine at all.

Tim

Thanks Tim, if you get nothing when you connect battery positive to the small wire at the starter then you have a bad solenoid or maybe a frozen solenoid?? If you have a voltmeter we can check power at the little wire when holding the key to start to be sure or you could try lightly tapping on the solenoid to see if it frees up.

 

Marty

Customer: replied 8 years ago.
Marty:
Typing is a bit slow here, due to no feeling in my fingers. You were brilliant. Don't know if it was the tapping on the solenoid or just the right connection to hotwire the starter. Whichever, it worked and it's running. Even if it doesn't start by key again tomorrow (which, I believe, will be a prety clear indication that the problem is with the neutral safety switch), I'll know how to get it running to get it to a repair shop.
Send me one more reply. I need to know how to insure that you get paid. Payment well earned, sir.

Tim

That's great Tim. I'm glad you got it going. Let me know if you need anything else.

 

Marty

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