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.

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Doug

1987 300TD x 3
2005 E320CDI

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?)?

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1989 300E 144K

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. )

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Either or both ?????


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

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

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.

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

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 ?

Anyone ?

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 ?