rotax_rave

4 years ago the "low fuel" light kept coming on and the fuel level gauge wasnt working. the truck died and we replaced the fuel pump. for the next 3 years the fuel guage worked and the truck ran fine for about 1 month the "low fuel" light was coming on and the truck died (at night) and would miss at 1500-2000 rpm - it only did this about twice in 5 days. so we replaced the fuel pump and the fuel guage works now. but driving up to a red light the truck died like it did a few days ago after replacing the fuel pump. it died when the headlights were on. it never died when the headlights were off or missed. had the alternator checked it was fine... thinking of replacing battery? there is also a voltage drop from 14.5 to 13 when the blinkers go and it goes to 12 when the windows are rolled up... so basically any electical load is dropping the voltage from 14-15ish down to 12-13ish. and when the headlights and brakes are on, the truck dies.

so its not the fuel pump it was just replaced. im thinking alternator or battery cause it never dies (yet) in the day with the main headlights on.

any help greatly apprecieated.

ukrkoz

well, it just darn looks like alternator. i donno how you had it checked, but you say it's ok. obviously, you still have low power supply to the system.
the way it operates, electrical system is designed to feed engine 1st, then the rest of the appliances. so, somehow you have it enough to "check out" and not enough to run under load.
my 1st guess is loose belt. check indexation marks on your tensioner. if it's next to the very far right one, facing the vehicle, or past it - you got your answer, replace the belt.
otherwise, have your alternator checked under load. and disconnect/clean/lubricate all leads on it.
i am not much of electrical guy, but common sense tells that, also, whatever is diverting electrical supply to various powertrain areas, might be mulfunctioning.
wild guess - power drain somewhere, starving your system. a shortned light bulb..., dirty terminals.... oxydized contacts....