Alarm Arming Switches

On my 1985 500SEC, the alarm arming and disarming switches in the doors are completely un-predictable. Sometimes the alarm will arm and be ok, most of the time it will sound when the door is opened. The trunk switch always works and will silence the alarm. Can the door switches be adjusted, or replaced without changing the locks? Or...do I just need to have the remote alarm and lock system installed? The master lock system works perfectly otherwise.

Help, this is driving me crazy having to use the trunk lock all the time.