Ford Repair: truck dieing, electrical loads, electrical load

Question
i have a 1987 f250 w/460 4sd the truck dies if i run two things at once like headlights turnsignal the truck dies any electicle combinaton new altator puts out good
HELP

Answer
Hello and thanks for the question...I'll try to help.
 Let me start off by saying NEW does NOT mean GOOD.
I would recheck your charging system and battery. The alternator might be charging OK at idle, but what about when an electrical load is applied?
You would want to check the base voltage...it should be between 12.3v-12.9v (with out the vehicle running). Next, have all electrical loads OFF, start the engine and bring the idle up to 1500 RPM---check the voltage again......it should be at least 1.5v OVER the base voltage. Next, let the engine idle at a normal setting and start applying loads to it......headlights, radio, defrost/AC, directionals......look at the voltage.....what is it? IF it has dropped, then most likely the regulator in the alternator is shot (remember--New does NOT = Good) Replace the alternator if it is not keeping up with the load being applied.
Hope this helps,
Erik