Hello everyone ,I have a 1986 NH LB-620 BACKHOE THAT IS GIVING ME A HEADACHE.FOR SOME REASON WHEN I START IT NOW ;I TURN KEY ON,HIT GLOW PLUG BUTTON 10-15 SEC 1/3 THROTTLE ,AND IT STARTS AND RUNS STRONG FOR ABOUT 2-5 MIN. THEN THE VOLTAGE GAUGE DROPS LOW,BARELY IN THE GREEN AND I HAVE NO CONTROL...