SC factory alarm bypass problem
 

Hi everyone,

I've tried searching but can't find my answer so am starting a new thread!

The factory alarm on my 1980SC started going off intermittently. I never have used the alarm and it's always OFF. I've since found that the drivers door latch/key seem to be the main culprit as I can trigger/slience the random alarms by pulling the lever or jarring the door by opening/closing it. I'm reluctant to disassemble the door to try and fix the latch and decided to try bypassing the alarm.

I jumpered terminals 61-61 and K1-15, which seems correct and the latter being analogous to the 87a-15 terminals I've found referenced in threads here. My alarm control unit looks like this one. The jumpers did silence the alarm, and the car does start and run, BUT I also got a quite loud, electrical-type whining sound from the engine compartment when the ignition is turned on that makes me think something is wrong, but I don't know what it is!

I've undone the jumpers and gone back to stock and am not sure what to do now... Help!!!

Thank you,
Brian

I think you'll find that the high-pitched whine from your engine bay is just the CD ignition unit. The metal box in front of the fuel filter on the left.

Probably it didn't seem so loud before, because you weren't so anxious about strange noises!

Hi, thanks! I'm not sure what is causing the "problem" sound (I stopped working on it tonight -- needed a break), but I know there is normally a whine sound that is probably the CD unit, but the new sound is **much** louder! It also sounds less regular, though that is hard to describe (maybe I can capture a video if needed). Also, I tried installing and removing the jumpers to make sure that is what is causing the difference, and I can turn the loud sound on and off with the jumper.

Brian,

Might be a stupid question, but did you remove the alarm relay permanently? You need to replace the relay by the jumpers not add them.

The jumpers 61/61 take care of the battery charging circuit being reconnected when the alarm relay is out and K1/15 takes care of 12V supply for the fuel pump when the ignition key is turned.

When the relay is in the socket and the alarm is activated by the alarm on/off key, the fuel pump and charging lines are interrupted to prevent the car to start and drive. All other other connection to the alarm relay are just used to control the alarm.

So with the two jumpers in the relay socket - with the relay removed - the car should start/run as if the alarm is switched of.

I hope this makes thing a bit more clear to you.

Otto

Alarm.
 

This should work.

Hi Otto, thanks for the feedback. NOT a stupid question. In all the threads I found on the bypass, I don't recall it being explicitly stated anywhere that the alarm unit should be completely disconnected, so I actually tried it both ways, but there was no difference.

I took two short videos (audio only) to record the very different sounds from the engine compartment. for reference, the camera was laid down by the gold stickers where the rear latches closed.

vid 1 -- stock, with alarm unit connected. You can hear me turn on the ignition switch three times, after I got in and closed the door (or the alarm would have gone off more). You can hear it go off momentarily as I open the car door to come back to the camera.

vid 2 -- with alarm unit disconnected and 61-61 and K1-15 jumpered at the wiring harness. You can easily hear how much louder the sound is. It is more of a buzzing than a whine. Also, the second time I turn the ignition, if you listen closely you can hear a second, lower pitched sound underneath the first -- this one is intermittent, and almost easier to feel than hear. The sounds makes me nervous and although the car starts (I tried it once), I'm afraid to drive it without understanding what is going on. Best I can figure the noises are coming from the top rear of the engine bay -- back by the sound deadening foam, but it's hard to be sure!


Another piece that may matter is I remembered that a long time ago (10 years?) I pulled some wires and a horn when I first got the car that at the time I thought was part of the alarm. It wasn't connected as I recall. In any case, I wonder if this suggests an additional system might have been installed on top of the factory alarm?? Here's a picture of the harness and horn that I removed.

http://forums.pelicanparts.com/uploa...1466474319.jpg

Thanks for your reply. I listened to both of your recodings.
The first one - The horn should not go off when you open the door. Imagine visiting at a Porsche meeting... Something will be wrong with the Porsche alarm unit. A broken wire or short in the alarm wiring harness could not be the cause of this alarm pulse. In that case it would go off and the car would not start. If no wiring is added to the alarm wiring harness, the alarm unit is faulty. Why did a PO replace the original alarm? Check if the wiring is complete and correctly connected. There should be someting wrong with the wiring otherwise there would not be the strange noise with the alarm disconnected.

The second one - Indeed a very nasty sound. It must be some electric device making the sound. It remembers to be a DC-relay connevted to AC. So what original devices are on the line between the decals to the sound deadening? Basically only the alternator and some other motor related parts having no relation to the Porsche alarm. I really would take look behind the sound deadening and listen/check under the parcel shelf cover if there is any additional equipment installed. Don't forget that it is always very hard to tell where a sound is generated. The lower the frequency, the harder it is.

The horn and wiring you showed in the pic could be from an after market alarm system. All alarm systems function in a similar way. They often use parts of the original wiring to get to door contacts, starter, alternator and/or other parts to sensor if someone enters the car and tries starts it. Again, this makes it important to check the wiring for the Porsche alarm.

Let me end with another "stupid" question: do you have the original instrument lighting or did you change to led for instance? The Porsche alarm sensors the alternator through the charging indicator in the dash. This could cause a failing alarm unit and - if the circuit is modified - cause a sound in the alternator through jumper 61/61. I agree, not very logical, but with electronics everything is possible.

I hope you will get a bit nearer to the solution.

Otto

Hi Otto,

Thank you for the thoughtful reply.

I know there is a problem with the factory alarm and I am pretty sure it is with the door lock since I can cause the alarm to chirp by just by pulling on the door handle's trigger (without moving the door). When I first posted this thread I was thinking it would be easier to just bypass the alarm than to disassemble the door, but now I am thinking I should try to work on the door and find/repair the loose contact there.

As you suggest I will look near the deadening panel to see if I can find anything that could be making the noise and report back.

The harness in the picture wasn't actually connected to anything so I'm not sure if it was ever installed. It was a while ago, so my memory could be wrong, but I think it was just loose in the trunk area. If it was connected that would add a lot more complexity to the system!

Lastly, my instrument lighting is stock.

Thanks again for the help!

Well I think I found the problem! It turns out one of the wires to the alarm key switch was exposed and almost broken through from contact with the locking mechanism inside the door. I repaired the wire and put everything back together and the alarm is not chirping at me anymore!!! Here's a pic of the damage:

http://forums.pelicanparts.com/uploa...1466558659.jpg

Fingers crossed when I get everything back together that I won't have any more issues. If so, I'll just leave the alarm unit connected as I found it.

Thanks again for the help!

Congrats Brian, these are indeed the original Porsche wires to the alarm key lock in the door. Let me say it is a poor construction so close to the door lock. Use some sticky putty to fix the wiring to the door and the same damage cannot happen again.

Nevertheless, it does not explain to me what the cause of the humming sound in the back originates. When the alarm relay is taken out, the wiring to the alarm lock in the door shouldn't be connected to any other electrical device. So my idea that there some connection between the original Porsche alarm wiring and some 'replacement' alarm wiring is still there.

I'm very curious if the Porsche alarm works as it should from now on.

Otto

Had a similar problem with factory alarm 10 years ago. Intermittent connection of alarm key switch. Alarm would sound for no reason - sometimes just a toot or two. Fixed wires, changed key lock as I had no keys to original switch and factory alarm has worked perfectly since.

I still haven't driven the car to be sure but I put everything back together tonight and no chirping while working on it and testing the door afterwards so I think the broken wire was definitely the problem.

Interestingly, I tried turning the alarm on with the key and it doesn't seem to do anything... I have never used before so I don't know if this is expected or not. I'm not complaining though! :)

I still don't know why the alarm bypass caused the abnormal sounds, but before I fixed everything I did determine that there were at least two different sounds. One came from the engine bay as described above, but the other was from near the front axle -- most clearly heard under the car. Oil pump?

I'm probably not going to look into this anymore since I appear to be back to normal now!

Thanks again to everyone, and especially Otto, for the help and comments!
Brian

Brian,

When activating the alarm there is no indication it is activated, so no sounds or control lights flashing like in modern cars. Open a door when activated and you should hear the alarm horn. Do you know that the original alarm horn is positioned on the cross bar between the front wheels (hidden by a cover plate) near the fuel pump? If the alarm doesn't go off, the horn might be defective or the wiring to the horn cut. Remember, for some reason they installed a replacement for the original alarm.

Good luck with the last bits of testing and reparing.

Enjoy your SC,

Otto