Some alarms systems have a protection function which will prevent starting the engine is somebody tried disconnect the battery and connect it again.
Also what might happen is that your alarm system doesn't have memory in the case if you disconnect the battery. Thus, if you do disconnect the battery it will reset the alarm system to the default factory settings. By default, the alarm system will block starting the engine.
To reset the alarm on a 1985 Mercedes 500 SEL, first, unlock the vehicle using the key in the driver's door. Then, insert the key into the ignition and turn it to the "On" position without starting the engine. If the alarm is still active, disconnect the battery for a few minutes before reconnecting it, which should reset the alarm system. Finally, ensure all doors are closed properly to prevent the alarm from reactivating.
remove negative battery cable for 2 min
With a scan tool or by unhooking the battery.
Just disconnect a battery cable for a couple of minutes.
Check It Out - 1985 No Cause for Alarm 1-3 was released on: USA: 16 October 1985
Virgile Reset was born on 1985-08-03.
The 1985 Lincoln Town Car fuel pump reset switch can be found in the fuse box. The reset switch will be at the bottom of the third column.
GM vehicles do not use inertia/reset switches
disconnect both battery terminals, then reconnect. This will reset onboard computer. battery must be charged to 12 volts or better
Cadillacs do not use inertia/reset switches.
If its anything like my 1985, the fender right behind the front left wheel comes off. There are 4 bolts in the wheel well, and one retaining bolt between the fender and the rocker. From there its just like changing a normal battery.
Unhook the battery for a minute. Once you hook it back up take the car for a drive. Preferably with several miles at highway speed to allow the computer to re-learn some of the settings.