1972 Anti Theft Alarm Problem
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7th Gear
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1972 Anti Theft Alarm Problem
Hi there, I'm new to the forum, I have a technical question regarding the Anti-Theft System on my Corvette, I hope someone can help! I have replaced the wiring harness with a replacement harness from 69-70, it connects at the switch at the rear, then grounds at the frame, it plugs into the horn (which is a replacement horn #12368067) it runs into the rear compartment where it connects to the relay and flasher which I have replaced the flasher and relay. The white wire connects to the front door pin switch on the driver side, the other white wire goes across to the passenger door pin switch. These switches are the front switches for the light not the rear of the jamb. The orange wire I have plugged into the battery slot of the fuse block. I did not use the connector for the ground to the wiper terminal as there was not a "prong" on the wiper motor so I grounded it directly with an eyelet to the wiper motor and continued the white wire to the hood switch. The problem is when I arm the alarm I have 12 volts at the horn and the relay gets hot. When I disarm the alarm it has 0 volts.
Another issue I have is I read somewhere not to ground the horn but if I dont ground it it will not sound at all, if I ground it as soon as I arm the system it wails. Any insight anyone can add will be extremely appreciated!
Another issue I have is I read somewhere not to ground the horn but if I dont ground it it will not sound at all, if I ground it as soon as I arm the system it wails. Any insight anyone can add will be extremely appreciated!
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From: North of Toronto - Ontario
I'm not that familiar with the 69-70 but on the 72 the switch is connected to constant power on one side (orange) and the other side goes to the horn (pink). The other connection on the horn goes to the flasher then the relay then ground so that the ground is controlling the on-off sounding
On the connection to the horn (pink) it keeps going to the relay as well
M
On the connection to the horn (pink) it keeps going to the relay as well
M
Last edited by Mooser; Jun 3, 2020 at 09:07 PM.
Thread Starter
7th Gear
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I'm not that familiar with the 69-70 but on the 72 the switch is connected to constant power on one side (orange) and the other side goes to the horn (pink). The other connection on the horn goes to the flasher then the relay then ground so that the ground is controlling the on-off sounding
On the connection to the horn (pink) it keeps going to the relay as well
M
On the connection to the horn (pink) it keeps going to the relay as well
M
Race Director
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From: North of Toronto - Ontario
The other thing is that they normally run off the rear door ajar switch and not the front ones. Even in the earlier ones????
M
M
Last edited by Mooser; Jun 3, 2020 at 10:11 PM.
Race Director
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From: North of Toronto - Ontario
Looking at this diagram what I see is... (a little different than the 72 but basically the same)
When the switch is turned on, the relay is read but not tripped
When a switch closes (door open) the relay is tripped, turns on and latches (stays on) and the flasher will provide ground to the horn through the yellow, flasher heats and stops conducting horn off, cools off and re-conducts horn on.....
M
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Race Director
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From: North of Toronto - Ontario
That seems to match the willcox image I put above but looking at it again, if the orange is connected to the BAT it's constant power and if the yellow is connected to the mounting bolt then the mounting bolt must not be "frame ground" otherwise the horn would go off as soon as the key was on.
I believe my description of how it should work is still correct
Maybe check and make sure you're on the switched side of the door/hood switches
M
I believe my description of how it should work is still correct
Maybe check and make sure you're on the switched side of the door/hood switches
M
Thread Starter
7th Gear
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I have the yellow grounded to the frame with the antennae wire. It is also grounded at the driver side pillar where its metal. As soon as I turn on the key the horn goes on, it does not pulse and the relay gets hot that's what is making me think I'm not grounding correctly somewhere.
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I'm pretty sure the yellow to the horn provides the ground to activate the horn and shouldn't be grounded. The horn mounting bolt can't touch the frame or anything grounded either
Yellow to the flasher and the horn only, if it's grounded anywhere (door or antenna) then the horn will go off as soon as the key is turned
Constant power, switched ground
M
Yellow to the flasher and the horn only, if it's grounded anywhere (door or antenna) then the horn will go off as soon as the key is turned
Constant power, switched ground
M
Last edited by Mooser; Jun 4, 2020 at 11:23 AM.
The ORIGINAL and bestest
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Quoting myself:
From this older thread:
https://www.corvetteforum.com/forums...t-working.html
I also offered some troubleshooting advice to the OP of that thread that might help you.
The alarm system consists of:
- a pin switch at each door jamb in the back (not the hinge side)
- a pin switch for the hood (located above the wiper door actuator)
- a latching relay in the passenger side rear compartment
- a turn signal type blinking relay located next to the latching relay
- a horn in the driver's side rear 1/4 panel (above the muffler)
- a key switch in the rear panel to arm and disarm the system
This is how it works:
1) +12v is fed to one side of the key switch on the orange wire
2) when you arm the system by turning the key switch, the other side of the key switch gets +12v, which also sends +12v to one side of the horn and one side of the coil of the latching relay
3) when one of the three pin switches is closed (by opening the doors or hood) they send a ground signal to the other side of the coil of the latching relay, which in turn latches the normally open contacts closed, which sends a ground signal through the blinker relay on to the horn, which then honks in a cycle like a turn signal light does.
4) the only way to disarm the system is to turn the key switch to the off position, which breaks the +12v being fed to the latching relay, causing the previously latched set of contacts to open. Once set off, the alarm will sound until disarmed, or your battery runs out.
The whole thing works off ground signals. It may sound confusing, but it is really quite simple. When I did the body off resto to my car, I found that the alarm horn's diaphram was shot and the blinker relay was shot. Replaced the factory alarm horn with one called "the freeway blaster" that I found at the parts store, and replaced the blinker relay with a new one, and it works like a charm. The pin switches are often not working, so you might want to check them too. the door pins are servicable through the access door located in the rear wheel wells in front of the wheel. These pins have three wires on them: ground, alarm, and door ajar light; they serve a dual purpose, set off the alarm and light the door ajar light. The pin switch for the hood gets its ground at the wiper motor.
Hope this helps.
- a pin switch at each door jamb in the back (not the hinge side)
- a pin switch for the hood (located above the wiper door actuator)
- a latching relay in the passenger side rear compartment
- a turn signal type blinking relay located next to the latching relay
- a horn in the driver's side rear 1/4 panel (above the muffler)
- a key switch in the rear panel to arm and disarm the system
This is how it works:
1) +12v is fed to one side of the key switch on the orange wire
2) when you arm the system by turning the key switch, the other side of the key switch gets +12v, which also sends +12v to one side of the horn and one side of the coil of the latching relay
3) when one of the three pin switches is closed (by opening the doors or hood) they send a ground signal to the other side of the coil of the latching relay, which in turn latches the normally open contacts closed, which sends a ground signal through the blinker relay on to the horn, which then honks in a cycle like a turn signal light does.
4) the only way to disarm the system is to turn the key switch to the off position, which breaks the +12v being fed to the latching relay, causing the previously latched set of contacts to open. Once set off, the alarm will sound until disarmed, or your battery runs out.
The whole thing works off ground signals. It may sound confusing, but it is really quite simple. When I did the body off resto to my car, I found that the alarm horn's diaphram was shot and the blinker relay was shot. Replaced the factory alarm horn with one called "the freeway blaster" that I found at the parts store, and replaced the blinker relay with a new one, and it works like a charm. The pin switches are often not working, so you might want to check them too. the door pins are servicable through the access door located in the rear wheel wells in front of the wheel. These pins have three wires on them: ground, alarm, and door ajar light; they serve a dual purpose, set off the alarm and light the door ajar light. The pin switch for the hood gets its ground at the wiper motor.
Hope this helps.
https://www.corvetteforum.com/forums...t-working.html
I also offered some troubleshooting advice to the OP of that thread that might help you.
Thread Starter
7th Gear
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Gents, I cant thank you enough. I removed the yellow wire from the frame and connected it to the horn and when I tested it everything worked like it was supposed to. I had been banging my head on the wall over this for a few days and it turned out to be something simple. I really appreciate all the insight probably saved me a bunch more days! to you guys.
to you guys.
Race Director
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From: North of Toronto - Ontario
It's frequently the whole - tupperware car - nothing is grounded by bolting it to the frame - separate ground wires needed for every light - lets use that as a wiring feature - PIA - thing that vettes have. When in doubt, first place to look is at the ground / lack of ground causing the problem
M
M
1967 Pedal Car Champion
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Gents, I cant thank you enough. I removed the yellow wire from the frame and connected it to the horn and when I tested it everything worked like it was supposed to. I had been banging my head on the wall over this for a few days and it turned out to be something simple. I really appreciate all the insight probably saved me a bunch more days! to you guys.
to you guys.Here's a generalism by SwampeastMike from a different thread that I wasn't aware of and maybe it will help you too:
https://www.corvetteforum.com/forums...post1601620502
The wire color coding in our cars is simple and reasonably consistent--highly consistent in the cabin.
Grey - Instrument panel, gauge, etc. +0-12V dimmable background lighting.
Black - Permanent chassis ground
Yellow - +12V power with ignition switch in "run"
White - Switched chassis ground.
Orange - Fuse protected constant +12V
Red - Constant +12V unfused (but with fusible links).
Purple - Fuse protected controlled +12V , ignition "on".
Pink with Black stripe - +12V ignition "on" power to gauges.
There are certainly more colors but their uses vary. Pink is typically +12V ignition "on" power associated with accessory items like power windows, rear defog, delay wipers, cruise control, etc.
Grey - Instrument panel, gauge, etc. +0-12V dimmable background lighting.
Black - Permanent chassis ground
Yellow - +12V power with ignition switch in "run"
White - Switched chassis ground.
Orange - Fuse protected constant +12V
Red - Constant +12V unfused (but with fusible links).
Purple - Fuse protected controlled +12V , ignition "on".
Pink with Black stripe - +12V ignition "on" power to gauges.
There are certainly more colors but their uses vary. Pink is typically +12V ignition "on" power associated with accessory items like power windows, rear defog, delay wipers, cruise control, etc.