Just a warning... If you think that insurance, garage, handgun or trunk monkey is enough to protect your car or you think that "a thief will get it no matter what so why bother" then this thread is not for you.

For the rest of you who are interested I have been thinking awhile about upgrades to the C5 alarm system. With the addition of the window valet and resistor in the key the factory system is pretty decent IMO. I would however like to add a loud siren to the factory setup. This is what I am thinking:

Using a relay tap into the horn power and wire up the siren. Easy enough though the problem is now my horn will fire up the siren all the time. Not good. So.... I was thinking of finding the (-) trigger for the horn switch at the wheel and using that to disable the siren relay. Anyone know where that wire would be? Or if it exists?

The only thing left would be to find a way to get the siren to stay on and not "beep beep" with the horn. I think I could live with it but it would be cool to keep the siren blasting the whole time and not come on and off.

Any thoughts CF? If I can pull this off I will post a complete procedure with pictures.

 

For hardware consider the Wobbulator V2 Siren. it's a 95W 120dB self contained blaster that's easy to hook up. features traditional wail and wobble tones. it's a steal of a price without the need for an external amplifier.

http://www.wfgear.com/prodtype.asp?c...earchCriteria=

There should be a way to tap into the alarm siren without going into the horn circuit.

 

Good luck with your new anti theft device

 

What do you mean by the alarm siren? The new one or the one I want to add? How would I power it without using the horn power?

 

Good luck - let us know what you come up with (and pics would help).

 

There's usually a seperate circuit if a device can be activated by multiple sources. (example: reverse lights, DRLs)

Once the alarm output to horn wire is found, you can seperate the wiree with a diode, and tap from the upstream portion to trigger a relay that powers the siren.

It's MUCH easier with an aftermarket alarm, but it should still do-able with the factory alarm.

 

When one of my horns died I looked for one here and on fleabay. Everyone wanted a fortune for one. Looked in the junkbox and found the right note horn and modified it to replace the defective one.

Happened to see an AOOGA horn at Harbor freight on sale for $9.99.
Purchased it and found an old relay from some other car also in my junk box. Mounted the AOOGA horn using the same bolt the other horns are mounted on. Ran wires from under the hood to the new fuse and relay (didn't want the current from the AOOGA horn to fry the C5 horn relay).

I originally was working on the horns as they wouldn't blow with the steering wheel switch. Was a blown fuse caused by the defective horn. In the process of problem determination removed the steering wheel and located the wire coming down the column and spliced into it.
Monted a small black almost invisible switch in the dash to use in case the membrane finally quits. Also installed a SPDT toggle switch with center off. One toggle is maintained contact and the other toggle is momentary contact. Wired this to the new AOOGA relay to blow the AOOGA horn only. Center terminal is used to go to the relay, momentary terminal goes to ground, maintained terminal goes to the wire coming from the horn switch which when grounded blows the C5 horns. The relay 12V is powered with a 20 amp inline fuse which also feeds the open contacts for the AOOGA horn.

Operation is as follows:

Witth toggle switch in the middle normal horn operation from either the membrane switch in the steering wheel or the added switch on the dash.
With the toggle switch in the maintained contact position blowing the horn also activates the AOOGA horn.
With the toggle switch depressed and held on the AOOGA horn blows as long as you press the switch.

If you leave the switch in the maintained position the AOOGA horn will sound along with the regular C5 horns.
This will allow it to blow when the alarm sounds.
Could substiutute a siren for the AOOGA horn and it could probably be mounted using the same bolt as the existing horns.

BIGHANK

 

Horn output from the BCM is black wire location B10 at connector C1. Adding a siren to the oem system is a good idea.

One thing I did to my factory alarm is remove the disarm connector inside the door that's activated by the key cylinder. This switch is a major flaw in the system. If someone uses a slim-jim or a flat screwdriver to break and turn the key cylinder, the alarm will disarm and unlock the door. The only inconvenience is if the key fob fails, alarm will trigger once you open the door but as soon as a valid key is put in the ignition switch, vats is disabled. I tried to make sure the disarm is not only controlled by the key sense switch (like a volvo S60 lol!) and its not. Adds a bit of safety imo. Here's a pic of the connector viewed from the top of the door with panel removed.

 

hmm i'll be in that area tomorrow working on my speaker plates.

did you just disconnect it?

 

you can add a motion sensor to the stock alarm also

 

Good post and info on the door lock cylinder. Question for you about the horn wire. Is that the wire that is from the wheel or is it just a (+) output whenever the horn blasts? Alarm or manual,

I have found the relay and after some testing I have found at least at the fusebox under the hood it pulses a (-) which triggers the relay to send (+) power to the horn via a green wire in the loom under the coolant overflow tank.

At this point I am leaning towards a hidden toggle switch/relay combo that will turn on an blinking L.E.D. as well as fire the siren when the horn honks. That way I just turn it off when I want a normal horn. I want to do as little cutting of the OEM harness and I can.

 

I just unplugged the connector from the latch mecanism inside the door. If you cut the blk wire from the output of the BCM your horn will still function as normal from the steering wheel. You can wire this output to a more powerfull and hidden siren. Output is negative pulse.

 

by negative pulse do you mean ground switched?

 

Awesome info! That is exactly what I want to do. Any change of posting a pic of B10 at connector C1? Oh wait, I do have the service manual I guess I can dig for it. The forum has made me lazy so post it if you have it

 

Also got info from the FSM:




(1) Sunload Sensor
(2) HVAC Module Assembly
(3) Air Temperature Actuator (C60)
(4) Vacuum Control Assembly (CJ2)
(5) Blower Motor
(6) Blower Motor Control Processor
(7) Fuse Block-IP
(8) Body Control Module (BCM)
(9) Ignition Switch
(10) Air Temperature Sensor - Inside
(11) Telescoping Actuator Switch
(12) Data Link Connector (DLC)
(13) Multifunction Turn Signal Lever
(14) Ambient Light Sensor
(15) Windshield Wiper/Washer Switch

Body Control Module (BCM) Connector C1:



Connector Part Information
12110244
24-Way F Micro-Pack 100 Series (PNK)

Pin Wire Color Circuit No. Function
A1-A2 -- -- Not Used
A3 WHT/BLK 1073 Ignition Key Resistor Signal
A4 ORN 1640 Battery Positive Voltage
A5 -- -- Not Used
A6 WHT 352 ALC HDLP Relay Control
A7 YEL/BLK 1138 DRL Ambient Light Sensor Low Reference
A8 -- -- Not Used
A9 BLK/WHT 851 Ground
A10 LT GRN/BLK 1137 DRL Ambient Light Sensor Signal
A11 -- -- Not Used
A12 DK BLU 1393 Courtesy Lamp Relay Control

B1 -- -- Not Used
B2 PPL/WHT 1074 Ignition Key Resistor Low Reference
B3 GRY 1901 Rear Fog Lamp Relay Control - Export
B4 DK GRN/WHT 1317 Fog Lamp Relay Control
B5 -- -- Not Used
B6 LT GRN 1037 BCM Class 2 Serial Data
B7-B8 -- -- Not Used
B9 LT BLU 1344 Trunk Release Relay Control
B10 BLK 28 Horn Relay Control
B11 -- -- Not Used
B12 GRY 2169 Convertible Top Relay Cover Release Control

 

Hmmm... I spent some time in the garage tonight and found the right wire, tested it with a volt meter and wired up my relay. After figuring out where the siren was going to mount I coiled up the wire next to battery. Then after securing the relay behind the bcm and cleaning up the interior I was going to call it a night... until I realized oh just for the heck of it I better try the horn and make sure it does not blow the siren. I wired up the siren manually and one push of the horn and there goes the siren.

So am I missing something here or did the Corvette Forum actually after four years give me bad information?? For the record I only spliced into the BCM black wire and did not cut it. If I cut it I have a nasty feeling that I will no longer have a horn anymore.

Please advise.... and tell me I did not just do all this work just to have to wire up a manual toggle switch in the ashtray to provide the +12 to the relay/siren. I just can't see how when I hit the horn the siren blows and if I cut the wire the horn will somehow find a way to work normally.

 

j84buick you're almost there! The steering wheel and bcm outputs for the horn relay are both common, so it makes sense that feeding ground thru the steering wheel will also ground the output of the horn at the bcm, and activating your siren. If you cut the blk wire from the bcm and leave it as a standalone siren output, all will work ok. Did you add a small fuse to the 12v side of your siren? Also the cone is facing down so it doesnt fill up with water over time?

 

No worries on the siren or fuses. I have installed many alarms and know the tricks.

Cutting the wire worked and the siren still worked just like you said. I am thinking though I may want to still have the stock horn blow with the siren.

Since using a relay I have converted that (-) pulse output from the BCM to a (+) pulse output to power the siren I am going to install a diode on the wire I cut so the horns will still fire when the alarm (and new siren) go off but the steering wheel will be unchanged.

 

A couple of years ago, there was a discussion on this site led by sk7 concerning adding a siren to the c5 factory security system. I recently purchased a c5 vert and have installed shock and motion sensors, and now want to install a siren. From what i have been able to learn, its a simple install using b10 alarm wire from the bcm. However, i need more specifics on the install. Any help/instruction/pics would be appreciated. Thanks..

 

I can tell you what I did above got the job done. The only negative is that since the horn pulses with the alarm so does the siren.

Are you familiar with relays and diodes? I had to use one of each to make the install work.