What is the problem with this code?

is working well when I give Direct Value as"'VIN__c='WAUZZZ8V3FA002049' ",But If I give dynamic Value as 'VIN__c=:setStrVINNumber" it is not working,Please have look the code in below:

String modelyear1;
String LMOI;
    // loop through all contacts to be updated 
  String setStrVINNumber;
    if(trigger.isBefore){
        if (trigger.isInsert || trigger.isUpdate){
            system.debug('-------333333-----1');
            for(Contact Objcont:Trigger.New){
               setStrVINNumber = Objcont.Id;
               LMOI=Objcont.Latest_Model_of_Interest__c;
            }
            system.debug('ID..........'+ setStrVINNumber);
           /*//////////////////////////////////////////////*/
           if(LMOI == null){
           system.debug('ID.......222222222222...'+ setStrVINNumber);
            for(Contact_Vehicle_Ownership__c objCVO : [SELECT Id,VIN__c,Name,Model_Display_Name__c FROM 
                            Contact_Vehicle_Ownership__c where VIN__c='WAUZZZ8V3FA002049' AND Customer_Vehicle_Relationship_Status__c='Active'])
               {  
                                       modelyear1=objCVO.Model_Display_Name__c;
               }
               }
               else
               {
              modelyear1=LMOI;
              // Objcont.Current_Model__c=Objcont.Latest_Model_of_Interest__c;
               }
               for(Contact Objcont:Trigger.New){
               Objcont.Current_Model__c=modelyear1;
            }

Please let me know if any queries.