I have a 2004 f150 fx4 5.4l, a while ago I was having problems with the front battery. I replaced it but right before it died I heard a clicking noise inside the cab. I have been trying to figure out the issue ever sense. Now the truck has no electrical power what so ever except for the aftermarket equipment I have running off the other batteries. The batteries are all good, ground is good, I replaced the fusible links (the 3 under about a 6" long plastic cover near the front battery, that's all 3 correct?) Still nothing. I checked to make sure the starter and everything is fine, the engine turns over but wont start completely. No power to obd2 port either to look for codes. I've checked various fuses I think could be related to the problem and no luck. Im getting really frustrated and would like some other input and ideas, thank you.

 

Welcome to the forum.

I would suspect the GEM module under the dash has fried. It is full of micro relays and controls most all electrical components.