Here's the deal: I have an 88 F150, 5.0/C6 EFI. It was acting up in rainy weather so I put some new plug wires on it - problem solved. I drove it on Saturday in the rain and it worked great. I didn't touch the truck until this morning when I went to leave for work, I tried the key - NOTHING happened, no radio, no fuel pump - absolutely nothing works except for my headlights and dome light. We had over 3" of rain here Sunday and the wind was blowing it around like crazy. I checked the battery voltage, it was 12.62V, I tried replacing the ignition switch (too cheap not to try) and it didn't fix anything. I checked ther connectors at the firewall - everything looked clean. It will crank over if your short the fender mounted starter relay so the battery is fine.

I hooked my meter to the fuse box in the radio fuse position and put the key in the accessory position - the voltage is all over the place from 1-12V, totally erratic. If I try the same thing in the run position, I get less than a volt. I'm a T&T mechanic and consider myself to be pretty handy electrically but this has me stumped. I looked in my Haynes book and I can't make heads/tails of the wiring diagram as everything seems to be inter-twined in some way, does anybody have any suggestions for something that I should check?.....I need to get this thing running as it's my daily driver - I gotta take my 63 Mercury to work in the morning so I still have some wheels but I'd prefer to leave that home and away from morning traffic.

 

Try replacing the starter solonoid. (Starter Relay). If it cranks when you jump it that is a good indication that is it bad.

 

When I have my key in the run position I have no power to my coil, accessories or anything. My fuel pump doesn't cycle either, I don't think the relay controls these too.

 

Check the fuse links @ the starter solinoid. I think it's the yellow that feeds the ing switch and the EEC relay. Without that you'd have nothing. I had to add a switch in mine for remote "kill", and brother it does it.

 

My ol' truck runs again.....It was one of the Yellow wires under the air filter box, one of those 3 wire joints Ford is famous for with no solder or frig all.....Geeesh.......Who thought up that bright idea?.....Run's like a champ again. I called my buddy at the local Ford dealership and a technician over there told me about the yellow wire joint under the air box too, apparently it's caused quite a few F150 owners grief....LOL....Note to self: Find the electrical engineer behind this fiasco at Ford and beat him senseless....

 

Glad to hear she's goin' again.