Euro500SLowner

The neutral safety switch from the automatic transmission for my euro spec 1983 500SL has a set of five electrical connection pins. I've been able to understand the purpose of the larger four, as follows: 50 and LP connect when the shift lever is in neutral or park, allowing the starter to engage, the primary purpose of the "safety" part of the switch. Also, a jumper between these two places on the disc shaped connector would allow an override of the NSS as a diagnostic for starting issues. Pins 81 and 81a are connected when the gear shift is in reverse, allowing the back up lights to illuminate. The square post has no electrical connection on the disc connector wiring harness, so may be a registration post only.

But the final smallest post at the top of the round connector plate is also an electrical connection with the disc wiring harness, but seems to have no electrical function independent of the position of the shift lever.

The existing NSS has part number 000 545 5306, but my replacement switch is 000 545 4906, which is identical, except that the small pin is missing. What feature might not work if I use the NSS without the small pin being present?

My manual is for US 107's so does not cover the 1983 500SL specifically, but when reviewing the wiring diagrams for those US cars, I see that the NSS is termed the "Starter lockout and back-up lamp switch". None of the US diagrams show a 5th pin in the switch unfortunately, just the two pins for neutral and park lock out and the two others for the back up light when the gear shift is in Reverse.

Euro500SLowner

Reference prior message

AlterSchinken

Here is some info from the 500SL wiring schematic. Pin S on the safety switch is wired to a relay that is somehow related to the kickdown system. It is called the "1st gear start" relay, so I assume under normal conditions your car starts off in 2nd gear.

Euro500SLowner

Beautiful! Your answer is right on target and explains the system. Yes, the 500SL will always start off in second gear, unless 1) you floor the gas pedal to engage the switch under the pedal or 2) you move the gear shift into the B or low gear position, which engages another switch at the shifter. Those are number 47 and 31 on the wiring schematic you provided. I didn't know how that was supposed to work, but I now see those switches trigger a solenoid that does the downshifting.

In the past, I've had a problem with the B switch sticking on the console even when the gear shift lever was moved away from the first gear position, and the transmission remains in first gear. Very annoying.

Where did you acquire the manual for the 500SL? I gather it is in German, so a problem for me even with Google Translate, but your knowledge seems to encompass both the language and the technical terms. A great and unusual combination. I pestered a friend fluent in German to translate the label on the fuse cover. I expect you would be amused at the result, which I keep in the glove box for reference when needed.
Again, many thanks for your reply to my posts.

AlterSchinken

The schematic comes from the German 107 site sternzeit-107.de, they have a lot of info but basically all of it is in German. They do have an English sub-section, but the hard data is limited.

My German comes from 35 years working as an engineer for a German diesel engine manufacturer here in the USA, you pick up a lot, especially technical terminology.

My '85 380SL has basically the same transmission as your 500, with some slight variations. One is that it starts in 1st, but still has the "B" and gas pedal switches and kickdown solenoid. The circuitry is far simpler, however.