What is the function of the Starter Lock-Out Relay? - PeachParts Mercedes-Benz Forum

locry · #1 12-05-2012, 01:24 AM

What exactly does it do?

I'm rewiring an S280 that was converted to diesel. Right now the car can be started by jumping the cables at the starter...

I have located the lock out relay and have confirmed 12V in key start position in one of the pins... but the relay isn't clicking. I opened up the relay and confirmed that it works. The positive pin that I identified does not correspond to the pin at the relay which triggers it.

I'm guessing it's because of the NSS? Where is that circuit exactly? Perhaps I can jumper it.

Anyway... first things first... "What is the function of the Starter lock-Out relay?"

If I can't use the original wiring... I can just jumper the Lock-Out relay to start via the ignition.... for now.

Gilly · #2 12-05-2012, 08:14 AM

My understanding is it keep the starter from engaging when the engine is already running. (theft deterrent may also use it)
The NSS I believe acts independently of the NSS, directly keeping the starter from operating unless in P or N, it is located on the transmission where the shift shaft enters the transmission, look at the pivot point of the shift laver on the trans.

mbdoc · #3 12-05-2012, 08:40 AM

100% theft deterrent. Only used for 3 model years, proved inadequate

Gilly · #4 12-05-2012, 08:45 AM

Thnaks, yeah I thought of that later, what prevents a reengagement is all in the key lock itself, has to be put back to "0" to engage into start position again. At least on the bladed key cars

locry · #5 12-05-2012, 09:48 AM

So it has nothing to do with the NSS? Cool. How can I bypass it? And where are the connectors for the NSS located aside from the one at the tranny? Where can I temporarily bypass the NSS?

The goal is to be able to start the car via the ignition switch.
Another thing... I know that jumping the starter positive lead to the solenoid runs the starter... But can I trigger the starter by placing a positive current on the SOLENOID from ANY source? what's the current draw of the solenoid? What gauge wire is safe?

oldsinner111 · #6 12-05-2012, 09:53 AM

a faulty ignition switch will do this also,To start turn to start and hold a minute or longer till she starts

Gilly · #7 12-05-2012, 11:13 AM

I really doubt the NSS is the problem and that jumping it will get you starting the car with the ignition. But if you were going to jump it you would jump it at the switch connector itself, not elsewhere on the car.

What year is the car????

locry · #8 12-05-2012, 11:55 AM

It's a 95 S280... yeah... where is the NSS connector at?

mbdoc · #9 12-05-2012, 12:00 PM

To bypass the K38 relay, simply jumper the terminals marked 30 & 87 on connector.

The NSS (neutral safety switch) is on the trans.

locry · #10 12-05-2012, 12:22 PM

30 & 87, so that's pins 2 and 4. Copy that!

From the trans... where does the wire of the NSS snake up to? I'd rather not go under the car at the moment... so if I can jumper elsewhere that would be great.

To backtrack a little... "I know that jumping the starter positive lead to the solenoid runs the starter... But can I trigger the starter by placing a positive current on the SOLENOID from ANY source? what's the current draw of the solenoid? What gauge wire is safe? "

Here's the situation... I installed a Diesel engine in a 95 S280, the car was submerged. So any and all electronics have been removed. I'm trying to get the starter to run VIA the ignition switch... ideally bypassing any and all unneeded circuits.

Here is what I've tried so far (aside from jumping at the starter terminals)... I have isolated the pin that goes to the starter from the X27 connector... and it does get 12V when the key is turned to "start"... I connected that wire to the starter solenoid... but nothing happens.

Zulfiqar · #11 12-05-2012, 12:40 PM

In a MB of that era - the starter solenoid wire is usually purple, the wiring plug for the NSS is also in the cabin It would have 4 wires, two for reverse and two for the starter, connecting both completes the circuit.

To test the purple wire going to the solenoid - dont use a multimeter, but use a headlamp if you can, if the wire can illuminate the headlamp at full brightness then it should also have enough amps to pull the solenoid. Otherwise you might need to add a hot start relay.

locry · #12 12-05-2012, 09:51 PM

Quote:

Originally Posted by Zulfiqar

In a MB of that era - the starter solenoid wire is usually purple, the wiring plug for the NSS is also in the cabin It would have 4 wires, two for reverse and two for the starter, connecting both completes the circuit.

To test the purple wire going to the solenoid - dont use a multimeter, but use a headlamp if you can, if the wire can illuminate the headlamp at full brightness then it should also have enough amps to pull the solenoid. Otherwise you might need to add a hot start relay.

Good info! I didn't realize that.
Both upper and lower harnesses have been removed from the car. The only wires that I have put back are the X27 round plug and the thick wires that go to the starter and alternator, which go to the positive block beside the x27 plug (under the car, passenger footwell) AFAIK I have connected the solenoid to the corresponding X27 lead. Am I missing something? It seems that lead doesn't have enough juice as you've pointed out.

locry · #13 12-06-2012, 12:06 PM

I finally got it to turn with the ignition... turned out the x27 was just a tad loose. All is well now. NSS has already been bypassed apparently(for now), upon my orders.

Confirmed it just now since I can start using the key.
Only thing to do now is to locate the NSS plug inside the cabin to put the NSS back into play when the car goes back into service.

Zulfiqar · #14 12-06-2012, 02:05 PM

in a W124 its near the accelerator pedal in a LHD car, the W140 should be similar as I dont think MB would route it over or under the transmission - the NSS on all older transmissions is at the left side of the transmission.

oldsinner111 · #15 10-07-2013, 11:10 AM

K 38 relay on a 98-99 is under the hood in relay box behind fuses.you'll see two modules then a row of relay starting from engine pink,black,little blue and pink.Pink one next to little blue is what you want to change,you can swap with top one if you are not using the AC.Car will start