Backhoe NH LB-620 issues

[alex 1375]

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 OF THE THROTTLE ANYMORE-MOVING IT DOES LITTLE TOO FOR THROTTLE RESPONSE, AND THEN THE ENGINE SHUTS OFF.CYCLE THE KEY,HIT THE GLOW FOR A SEC ,THEN SHE FIRES UP FOR A COUPLE OF SECONDS AND SHUTS DOWN,ON AND ON.I HAVE CHECKED FOR WATER IN DIESEL TANK BY POPING THE DRAIN PLUG-A LITTLE SEDIMENT,RUST AND SOME DROPS OF WATER.NOT ENOUGH TO KEEP STALLING THE ENGINE AND NOT LET THE ALT. CHARGE! THE MECHANICAL FUEL FUMP FELT ON OCCASION FOREVER TO PRIME,SO I WIRED IN A 4-7 PSI ELECTRIC PUMP,CLOSE TO THE TANK ABOUT A FOOT AWAY AND I'M STILL GETTING THE SAME THING! THE BATTERY IS MAYBE OVER A YEAR OLD ,BUT LESS THAN TWO.AND THE ALTENATOR IS NEW ALSO.IVE BEEN CHECKING ALL GROUNDS,CONNECTIONS,PLUS I HAVE AN OWNERS MANUAL WITH WIRING DIAGRAM ,THERE IS NO FUSE BOX-ONLY 2 15AMP CIRCUIT BREAKERS 1IS FOR THE ELECTRICAL SYSTEM-SENSORS,STARTING,CHARGING.THE OTHER IS FOR THE BLINKERS,4 WAY AND WORK LIGHTS.I HAVE A FEELING IT MAYBE RELATED TO THE GAUGES OR THE CONNECTORS FOR HARNESS.IS THERE ANY SAFETY FEATURES IM MISSING?I KNOW I CAN START IT IN GEAR ALSO, AND I DISCONNECTED THE TURN FLASHER RELAY AND LIGHTS,IT NEEDS ALL NEW LIGHTS ANYWAY.ARE THOSE HARNESSES KNOWN FOR PROBLEMS?THIS IS MY OWN AND I USE IT ALL THE TIME ,ITS REALLY JAMMING ME UP.ANY SUGGESTIONS PLEASE!!!!