Short or worse

[pullinpower350]

i have a 2003 f550 dumptruck with 22000 miles on it. ran fine until today. i went out to start it and no dash. then the dash came on but was flickering and wouldnt turn over. i did some trouble shooting and pulled the abs fuse. the truck stated and ran fine until i put the heater on. it started missing the shut off, no dash again, and no lights. now sometimes i can get it to start and sometimes it wont.. it did get some work done on the plow stuff as far as wiring and some welding. could it be shorted from welding or maybe a bad power breaker? this is really puzzleing me and i need the truck so anyhelp will be great. thanks