Thanks AWOL,
I removed the initial values from the header file, as you suggested. That did not remedy.
Here is the code for the updated header file:
/* FILE: multi_file.h */
#ifndef multi_file_h
#define multi_file_h
#include "Arduino.h"
extern byte var_1;
void fnc_1( void );
extern byte var_2;
void fnc_2( void );
#endif