Alarm wont turn off - 1988 Toyota Celica Liftback

disconnect the alarm to see if problem still there.

Repair your vehicle right away. Just click on the link I attach 2005 Chrysler Sebring Sedan Workshop Service Repair Manual

Start the vehicle with the key. Also try unlocking the vehicle with the electric locks. Either should fix the problem.

the wire from the horn is part of an imobiliser so it wont start replace wire it sounds like imobiliser battery or alarm pad if wont turn off

insert your door key into the drivers door when the alarm is going off;
turn the key and the alarm will reset

If the alarm is aftermarket I would remove it , I see this problem several times a month , take a test light and test for power at the starter signal wire while someone turns the key to crank this is the small gauge wire going into starter,if there is no power at this wire it will not crank ,if you momentarily apply voltage to the starter signal wire it will crank( also check starter signal fuse)(most alarm systems have a starter interrupt system ,and the aftermarket alarms fail after a few years) Alot of people believe there alarm is factory because it was there when they bought it new but dealer do add alarms that are aftermarket to please there insurance companies

Try "cycling the key in the passenger door lock. Turn it all the way to the right and all the way to the left.

try turning the key on then taking the +side off then turn key off and reconect+

try unhooking the battery while the battery is disconnected turn the ignition on leave the ignition on while you reconnect the battery this should override the alarm

something not reconnected