1984 c4 vette security light stays solid and wont start
Thread Starter
2nd Gear
Joined: Sep 2025
Posts: 2
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1984 c4 vette security light stays solid and wont start
I just bought a c4 1984 vette and after I bought it the security system suddenly went off. We got the horn disconnected and the battery disconnected now the security light won’t go off from being solid and the horn won’t work when we plug it back in. I’ve checked all the fuses. The fuses haven’t went bad I don’t know what I could be.
Pro
Joined: Jul 2023
Posts: 541
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From: Marysville WA
The first thing to try is unlocking the door with the round key. That should turn off the Theft Deterrent System. I had this happen a few weeks ago while having new tires installed. The tire techs somehow tripped the alarm and I had to go into the service bay and perform the above procedure.
Thread Starter
2nd Gear
Joined: Sep 2025
Posts: 2
Likes: 0
The first thing to try is unlocking the door with the round key. That should turn off the Theft Deterrent System. I had this happen a few weeks ago while having new tires installed. The tire techs somehow tripped the alarm and I had to go into the service bay and perform the above procedure.
Oil Producer
Joined: Apr 2014
Posts: 9,377
Likes: 2,737
i had this. i covered the fix in my frostbite 84 thread. i will see if i can link to it.
long story short, the theft detterent module is likely fubar. in our case, it was melted, triggering the starter disable relay and also the horn.
the PO got around it by jumping/bypassing the starter disable relay by jamming the relay closed, and unplugging each horn. Because the horn was always on, the horn relay melted. Who knows how long it was like this.
I may have the “starter disable relay” backwards with a “starter enable relay”. they reversed somewhere i think in 85.
It is also possible that the theft deterrent alarm off/disable switches in the doors/kelock cylinder is not properly rotating and therefore the suggestion to unlock the doors with the key is not working.
I do think u could test this by unplugging the battery. That should reset the alarm. Then do not lock the car. not with the key nor the power lock switches. just dont lock it.
Does the horn still blare and it still wont start? If so, probably a toasted theft derre t system module, and maybe your horn relay is also fried.
the tdm is beside/above the ecm and was masking taped to the wiring harness. look it up. remove the pass seat, the pass kick panels, get on your back or twist/contort i think its 2x10mm hex head screws to drop the exm. Then find that tds module. replace it. might see burn marks.
your horn relay is behind the information cluster with the toggle switches and the idiot lights. need to remove the dash left to right. will need to tilt steering wheel down and then remove the tilt lever. can also remove the screw along the rearward underside edge of the dash pad and then gently flex it up and all the panels will come out nice. be patient. save tour phillips screws.
long story short, the theft detterent module is likely fubar. in our case, it was melted, triggering the starter disable relay and also the horn.
the PO got around it by jumping/bypassing the starter disable relay by jamming the relay closed, and unplugging each horn. Because the horn was always on, the horn relay melted. Who knows how long it was like this.
I may have the “starter disable relay” backwards with a “starter enable relay”. they reversed somewhere i think in 85.
It is also possible that the theft deterrent alarm off/disable switches in the doors/kelock cylinder is not properly rotating and therefore the suggestion to unlock the doors with the key is not working.
I do think u could test this by unplugging the battery. That should reset the alarm. Then do not lock the car. not with the key nor the power lock switches. just dont lock it.
Does the horn still blare and it still wont start? If so, probably a toasted theft derre t system module, and maybe your horn relay is also fried.
the tdm is beside/above the ecm and was masking taped to the wiring harness. look it up. remove the pass seat, the pass kick panels, get on your back or twist/contort i think its 2x10mm hex head screws to drop the exm. Then find that tds module. replace it. might see burn marks.
your horn relay is behind the information cluster with the toggle switches and the idiot lights. need to remove the dash left to right. will need to tilt steering wheel down and then remove the tilt lever. can also remove the screw along the rearward underside edge of the dash pad and then gently flex it up and all the panels will come out nice. be patient. save tour phillips screws.
