Hi gang...My 86 F-150 4.9L 300 Six....Was running fine, UNTIL A raining snowy freeze overnight...ALL electrical Dead. [ Has new battery] I banged around under the dash... I got her running fine BUT IF YOU TURN ON LIGHTS, OR HEATER, OR WIPER, OR TAP BRAKE, EVEN A TURN SIGNAL. SHE WILL SHUT OFF AS IF YOU TURNED OF THE IGNITION? THEN, EVERYTHING WILL BE DEAD FOR A SPELL. I AM THE ORIGIONAL OWNER OF THIS TRUCK AND KNOW ALL ITS HISTORY AND REPAIRS.

I REPLACED the ignition switch, battery. when I got her running I had 14.2 V across battery.[13.5v engine off].

Could it be the starter relay [only 2 years old] would that short out/kill ignition,lights, acces, ect?

Could the computer cause this Killing of all electic power.[tho it will run like a dream if THE RARE TIME it starts/ electricals come back? HELP!

 

Have you had the alternator tested to see if it is bad?

 

Sounds like you've got a battery cable issue.

 

you probably have a bad alternator, you can get it tested for free at most auto parts stores

 

This thread is so old, that clunker's probably long gone!