My 1993 300E 2.8 starts fine most of the time, but sometimes it does not. the starter will move the engine just fine but there is no electrical current to the sparks plugs. this happens when trying to start with the radio & A/C on. now the weird part is that if the A/C is turned off it will start just fine. also, if the drivers side door is locked and unlocked it will start alright. i think it has to do with the alarm system cutting current to the engine. any thoughts?