I have a 1994 Cummins and yesterday a went to start it and had to jump start it. After it started my lights inside and out got weaker and weaker until they didn't work. I turned the corner and my truck decided to die in the road. I had no power anywhere. I just replaced my batteries 3 weeks ago. I pulled the alternator today and had it checked. It tested good. If anyone has some input on what it is i would really appreciate it.

 

fuse able link maybe i know when i had an 89 ford gasser that happened and the alt was fine then i noticed a wire burnt in half and the parts guy told me that wire was a fusable link replaced it and everything went back to normal. i dont know if they still use those. check all wires coming of alt trace them to all the charging parts and check fuses. including battery cables if there corroded then they coul;d be corroded inhalf inside the rubber insulation

 

ok. thank you i will check that out

 

Check your grid heater inside the intake horn. Sometimes they can short out and suck a lot of power fast.

 

check the crank sensor, if it goes out pcm wont see rpm signal and will not energize alt. to charge

 

When you replaced the batteries are you sure you hooked all of the wires to the battery cables back up ?

 

Ya, I hooked the cables up properly

 

Voltage regulator???...

 

Best way to diagnose stuff start with the obvious And easiest

 

I am having similar problems, but my truck did not die...just no lights/voltage. I started at the alternator, wired in a external regulator and that fixed it for a week...no im guessing its the Crank Position Sensor....Try these hope it helps