Friend has a 93 f350 and the pickup instantly dies when u pull the headlight switch anyone have any ideas on where to start on this turd??

 

I would start with a wiring diagram. Has anything ,alarm, radio etc. just been installed.

 

No nothing new electronic wise

 

What engine? Does everything go dead? Have you che kex battery voltage while it is running then as you turn the lights on?

 

12.7 while running but as soon as I pull the switch its like I **** the key off. It was the fuel injected 460. Everything else stays on it just kills the engine I haven't checked it is someone pulls the switch. It also melted a fuse labled std5 which is o2 censor heater, parking lamps and some other stuff but it didnt pop the 15 amp fuse just melted one side of the fuse

 

12.7 volts when running tells me the alternator is not charging the battery.
it may be a bad alternator, bad voltage regulator, or a bad fusible link.
i think it is dying because the headlights are drawing enough power to cut off the ignition momentarily.