Ive never had trouble with the alarm on my 1985s Euro until the battery went bad due to sitting for some time. Also there was some moisture in the car during this time. I was able to jump the car two times without issue and when I was trying to jump it the third time with hatch open and doors unlocked the alarm went off as soon as I turned the key in the ignition. Since that one time, the alarm will not disarm. Every time I open a door the alarm goes off. Using the key in the ignition sets off alarm. (I ONLY HAVE THE LONG KEY)

Since then I have replaced the battery. I have tried locking and unlocking all doors and hatch and it will still not disarm. Both doors will lock and unlock the other with the key. Both doors will turn off the alarm if I move the key to the unlock position. Opening the trunk with the key DOES NOT set off alarm. Moving the key to lock position in hatch does not activate central locking (cannot lock car from hatch). I have removed the hatch lock and disassembled the switch, cleaned contacts, and reassembled and tested OK with a multimeter and the symptoms are the same. All interior lights function properly and come on when supposed to. Opening the hood sets off alarm.

Any thoughts would be appreciated.

The thing I cannot understand is that opening the hatch with the key does not set off alarm, but opening a door does; even though both door switches appear to work because moving the door switch to unlock with the key turns the alarm off. But it obviously doesn't disarm the the system, because even if you get the horn to stop, when I turn the ignition it is no start and horn goes off again.

 

You might look into the alarm module. It is separate from the fuse panel. I think you can get new ones. Maybe a used one. My '80 had a no-start problem that was cured by changing that module. I don't think it was acting up quite like yours but it was changed by the PO because it was causing problems. Here is a thread that might help:

https://rennlist.com/forums/928-forum/203886-factory-alarm-system-as-source-of-problem.html

 

I'm going to guess that there's a short in the alarm switch wiring.

It sounds like it's arming all by itself.

As far as the hatch goes, does opening the hatch turn on the interior lights? It should. If opening the doors sets off the alarm, opening the hatch should too. Does it set off the alarm to open the hatch with the inside release button? (presuming those work)

And I don't think the hatch lock will activate the central locking. My 85 does not do that.

You can bypass the disable feature by crossing a couple plugs down on the CE panel. Not sure which ones, it varies by year. It's listed on here somewhere.

 

http://www.clarks-garage.com/shop-manual/elect-23.htm

The link above is the jumpering instructions that were in my glovebox from the PO. He used them to jumper the alarm module and said it worked. Then he replaced the whole module. The instructions are for a 944 but apparently its the same process for the 928. Luckily I have not had to mess with it but the instructions and jumper wires are still in my glove box just in case. Again, not sure if this is your issue but it might help.

 

Opening the trunk activates the interior lights as normal. Operating the remote hatch release does not activate the alarm. Im thinking that the alarm brain is fried. I will look into getting a replacement. In the meantime I am going to bypass. Whatever the fault is it is a sudden failure. It was fine until it wasn't. So I'm guessing the control module got fried with the low voltage from the bad battery and/or with the jumping voltage.

thanks for the info BlauerStahl, that is helpful and I will get on it as soon as I can.

 

Does anyone happen to know the location of the control module for the 1985 928s ROW? Looks like most people jumper the module at the level of the fuse panel, but Im going to find the module to either fix the original or get a good used one. A lot of posts that Ive read where people jump at the level of the control module show that the module is behind the glove box, but as far as I can tell the location is different by year and/or which side drive. I saw one post for a '90 RHD car and the module is behind the glove box. Mine is '85 LHD euro, so....any help appreciated. Thanks

 

The location of the control module for the alarm system in a 1985 ROW 928s is behind and above the glove box. Will post pics a little later. Gonna make a jumper and post results.

 

Well I almost set the wiring harness for the control module on fire. Connected just as instructions listed here:

http://www.clarks-garage.com/shop-manual/elect-23.htm

My guess is that the 944 wiring is different and those instructions will not work for a 928, even though the part number for the control module are the same.

 

https://rennlist.com/forums/928-foru...f-problem.html

Jump as in post #7 from above thread worked.

No alarm and car cranked, no smoke show.

 

Good, glad you solved. Virtually nothing is common, wiring diagram wise, between the 928 series and 944/S2/51 cars. And most 928 years are different from each other. Get a copy of special cd set from 928srus that has wsm, wiring diagrams and very important wsm supplements and tech spec books. This site is useful, but search really sucks. Use google to search topic by also referencing rennlist 928 forum. There have to be 50 alarm threads posted since the old one referenced. There are other ways to jumper it, but that way works.

Also, 944 series have Clark's garage; we have Dwaynes garage. Has some brilliant picture tutorials for certain returns for mid year and earlier S4 928s.
Lotsa smart people here, some of them true specialized 928 wrenches, several doing it for a living. Best forum ever!