why want my alarm arm on my jeep it worked when i first bought it

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i have a 98 jeep grand cherokee when i purchased it the factory alarm worked when i locked the door before exiting the light would start flashing and the alarm would be armed then it started only arming every once in a while now it want arm at all i purchased a key fob and had it programmed at dealer and it works great it locks and unlocks my doors and has a panic button that works to but the alarm still want arm when the alarm would arm the interior lights would go directly out now they stay on for a short period of time then cut off but it doesnt arm the alarm and advice would be helpful thanks in advance...Bobby