Need help car will not start !
 

Here is the situation. I have a 1990 Mercedes 500SL and is is currently not starting.

I had driven the car with no problems all last year and parked the car for the winter, but forgot to disconnect the battery and the battery drained completely.

Installed new battery and it will not fire, no cranking whatsoever. The battery is fine, as well as all the fuses.

Any suggestions ?

Corroded ground strap? Have you done an amperage draw test on the 2nd battery? Maybe it too is discharged. I have seen it before.

Installed new battery and tested, it is fine. All in grounded properly as well.

I also checked the overload protection relay fuse and that is not blown. Any other suggestions ?

Tempting the obvious : Have you tested the starter? Do you have power otherwise (ie windows, radio and stuff works?)?

I have not tested the starter no, but i cannot see this being the problem as it was perfectly fine prior.

I have all other functions that the battery should produce yes ( lights, horn, etc. )

<<and it will not fire, no cranking whatsoever>>

Either or both ?????


Try "N" position on shifter...............

No cranking at all and no sign of it even trying to fire. I tried starting it in N and still nothing.

maybe the ignition switch ?

<No cranking at all and no sign of it even trying to fire.>>

Well , if it does not crank, then it certainly can't attemp to fire ...that is what was confusing about your complaint.
Your complaint is the car does not crank, meaning the starter circuit does not engage.
Do the dash lights indicator lights come on when you turn the key to RUN position?

Yes, all of the indicator lights come on in the run position

On the W123 diesels there are easily accessable terminal block that can be jumped across so the motor can be turned over from the engine compartment while adjusting the valves. Maybe the W107 has the same feature? This would allow you to bypass the ignition switch.

Do this bat cable/terminal test:

Turn on headlamps.
Turn key to Start position while you or someone watches headlamps.
Do they stay lit when key is in stat position??????????????/

I'll try that later this afternoon whne I am at the car. What will this tell me ?

If the starter solenoid is getting power it will draw amperage and cause the lights to dim significantly. If they dim, then the starter or solenoid is bad, or frozen.

It tells you if the cables or bat teminals have a poor connection under LOAD
[ caused by starter motor draw/load] ..it is just a quick tech trick before we go into wiring circuits.
Just for info, You have a 129 chassis

Sorry for stepping on your post Arthur. Won't it also tell you if the starter or solenoid are bad?

Thanks guys, I'll try that and post here the results shortly after

I am not there yet. That depends on his report back. I do these post from the bat. feed foward. It is a diagnostic step sequence I use b/c many here are not Techs. If the light go Out , we have a connection problem cause by load. That is very possible with his condition, specially after sitting.
Both fuses 5 and 6 should also be spun in there holders , but iIdo not want to go there until we see where we stand with power feed.

No Crank
 

Have you tried cranking th engine with the shifter in neutral?
Is the car equipped with an aftermarket alarm? I've seen the starter interupt relays fail.
Good luck, Mike

I have tried to crank it with the shifter in neutral yes, no difference. It has no aftermarket alarm either, just the stock MB security system.

unless someone already mentioned, try arming and disarming the alarm again- I've seen that cause problems before too, try from different tumbler positions as well.

Just remembered this as well. The key is not unlocking the doors manually, but when using the remote to lock / unlock it's fine. Maybe this has something to do with it ?

I just did this and the headlamps stay on and do not dim at all.

NO conection
 

If you did not get any dimming of the lamps than you are not making connection to the starter,at some place in the system you are not getting current flow,I dont know enough about your car but if you have an alarm disability and the key is not working I would look in that area.:silly: j-n-t

OK
B/C the lights stayed On and no crank means that there is no starter circuit
being energized, thus you have passed the load/bad connection test .

Two more test.

First Test
With left hand , hold key over to start position while moving shifter on both sides of the N position. If it cranks, the problem is in the NSS. [ Neutral Saftey Switch]

Second Test
Spin the fuses for the K38 relay [ alarm interlock] I don't have that fuse chart handy, but I think it is 5 and 6 or 6 and 7. Spin those fuses in their sockets. If there is a poor connection at the fuse, the relay is not getting power and that would interupt the starter circuit.

Arthur,

I appreciate the help very much.

I just did both of these tests. I hope I did them right :confused:

First Test: I did this and still no crank.

Second test: I spun both 5 and 6 and also 6 and 7. What am I looking for here ? Still no crank. I am assuming spinning the fuses all the way around correct ?

The spinning of the fuses is to clean the connections at the tip of the fuses ...Benz fuses are notorious for making bad connections at the connection ends, specially after sitting for long periods. You should do them all.

If there is a poor connection there, the inerlock relay gets no power and on the factory alarmed systems, the relay has to have power when the alarm is OFF. It is in the series chain of parts for the starter circuit. The starter circuit goes from Bat to ignition sw, to NSS switch, to alarm interlock, to starter solinoid. Any break in this series results in a No Crank condition.
I do not have the 129 schematic here at the moment , so I am unsure of which fuse feeds that circuit. See if your chart has that info. Might be referred to as ATA

I spun every fuse on the car, and still no difference :(

Any other suggestions ?

Anyone ?

It sounds like the starter to me. Its a common problem for cars that have been sitting for a while. Try getting a testlight and checking if the starter is getting power when you turn the key, if it does then I would put in a starter.

I have tried everything you can think of to get this car started and still no luck.

I have a hunch is has something to do with the key. I have the master key for the car and the car will not lock / unlock manually. It simply will not turn the tumblers.

When I use the remote to lock / unlock it's works great. Also the MB anti theft system will only work one out of 5 times or so. ( arm system and open door and most of the time the siren will not go off )

What can be causing this problem ? Do I need a new key ? Any suggestions would be appreciated. I cannot tow this vehicle to the dealer due to the ride height!

Thanks in advance.

I would suspect the alarm relay contacts.
You may want to try arming the car several times rapidly and retry start. That may help clean off the contacts..or the relay may even be bad

I do not have a 129 chassis schematic , so that is hampering the diagnosis..I have most all others
Maybe someone here has one??????????????????

This would cause the no start problem I am having ?

Yes

The circuit for starter is bat > ignition sw > Gear selector sw > alarm interlock relay.. Any part/break in that series chain and the starter circuit is inactive.
That is why we talked about the gear selector being in N . That is a common fault for your condition, along with the interlock relay and the fuse that feeds the relay.
Each part has to be traced and checked via the wiring diagram.
Anyone have a 129 schematic?????????????

Is there a way to bypass this alarm interlock relay ? Maybe temporarily ground it out ?

I finally got the car into my shop to diagnose the problem. Went through all of the possibilities mentioned and came to this:

The shift knob on the center console has power running through it for some reason. I'm positive this is not normal ? When moving the shifter in and out of gear ( with the key to the on position ) it makes a clicking noise and the engine light comes on.

I've tried getting to neutral safety switch, but cannot seem to access it easily. Any suggestions for me ? The car will still not crank at all.

I would check to see if applying +12 directly to the starter, or terminal block gets it going. I would then suspect a bad alarm, unless of course you have a kill switch that you forgot about over the winter, because it sounds like no juice is getting to the starter.

good luck

Got the problem figured out finally !!! It was a loose transmission ground.....