I am running through diagnostics with the very patient help of A. Dalton. We have covered testing fuses, battery, x27 x49 and are up to pulling the instrument cluster to check k38.
Before I did that I wanted to post what i discovered this morning about the ATA system in hopes that someone my have experience that would help me.
The ATA led would not arm from the driver's side door. Today i discovered that it will arm (start flashing on the dash) from the rear hatch and from the passenger side door. The drivers side door will not disarm the alarm. IE if i unlock the driver door and open the alarms go off. However if i then close the door and lock it the alarm is disabled. Both the passenger door and hatch will arm and disarm the system. I tried cranking each time between arming and disarming by various doors but still no crank. At least I know the ATA led is powered now.

IF you want the car to start?? then by-pass the starter interlock relay (K38). then regardless of alarm operation you can still start the car!

MB only used that system for 3 years & figure that IT just didn't work.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

MB Doc, is this what you have in mind?
A Dalton wrote:
The starter draw is too much for the k38 contacts to handle , but they will handle the low draw of a test lamp or meter.

My suspect is the k38 and the cluster has to be pulled to get to it.
The terminals you want to jumper there are 1 & 3, which are relay terminals 30 and 87.

That will eliminate the K38 from the starter circuit.

You also have a ATA problem that may or may not be the reason for the K38 not working, but that is another story. I still would recheck all fuses to see if you can get the LED ARM lamp to come on..did you check the other ATA fuses I mentioned?

I also would like to be sure your battery is up to full charge.

Most guys that have ATA failure just jumper the k38 permanently by soldering a jumper across the K38 terminals 30 and 87 on the relay and plug it back in and be done with it...you only loose Alarm starter interlock.

Yes.

The K38 rarely fails! Most common problem is lack of signal from the ATA computer.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

So..soldering a jumper across the K38 terminals 30 and 87 on the relay and plug it back in
might allow start even if lack of signal from ATA computer?

Yes!

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

[QUOTE=M.B.DOC;
Yes!

Ditto...

...maybe a few more other opinions and you will do it .!

__________________
A Dalton

AD. I'm not second guessing you. I am very grateful for all the time and help. I did not want to annoy you with the business about the ATA and the driver's side door. Just thought it couldn't hurt to provide the info. I'm a bit daunted by pulling the instrument cluster, but I did order the special hooks from fast lane yesterday. I will put in a new battery today (though I'm not hopeful since I hooked up my big boat battery with 850cca and no start).
As soon as I get the tools I will pull the cluster. Is there any point in testing the ig switch while I wait for the tool? Thanks again sincerely.

< As soon as I get the tools I will pull the cluster. Is there any point in testing the ig switch while I wait for the tool? >>

I know that the cluster is where you got scared off, but it is not a big deal and there is no way to get to the suspect K38 without doing so...

But , aside from that, I also do not suspect the battery either b/c if the bat were too low for starter activation, then your jumper to X27 would not work... which is why my very first post sent you to x27 test........................ again, you did report low voltage to x27 when turning the key,so that is an indication that you do have a poor connection thru one of those parts [ K38 or Ign sw]. When the cluster is pulled , the ign feed to k38 is terminal #1 [ V wire] at relay 87. The power then goes thru relay to 30[ V/Grn]...that goes down to x49/2 which is NSS [ but you have already jumpered NSS , so we know your problem is up at K38 or ign feed to K38]..so.cluster time, no way around it.
I have seen a condition simular to your where the contacts in k38 were causing a poor contact and a new battery was sufficient enough to overcome the poor conductivity of K38 for start, but it was only a temp fix and k38 had to be change a few days later . I do not think that to be your condition and that is why we are looking at K38.
I also do not think that ATA is at fault for not energizing K38 b/c you started that you saw 11v at x27 from key...if k38 was not on, it would be impossible to see any V at x27. That is what K38/ATA does..it interlocks/interrupts power to X27 so a crook can't start your car.
You have some conflicting info that I am working with, but even thru that, I am satisfied that K38 circuit has to be looked at to finally get to the correct diagnosis... that test will be the tell.........and you can post this in any other post for other Techs/Members opinions, but I think you will get the same test procedure and sequence as I have done form the get-go.......Period.

I would also agree with MBDOC that once you are finally at the K38, I would jumper it permanently regardless of what you find just b/c of that chassis frequent failure rate of ATA/K38 activation......it is going to leave you stranded sooner or later ..[ but with the x27 jumper trick, at least you will now know how to get home...]

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A Dalton