Ok so I have an 03 f150 XLT with the 5.4 liter 2v engine and I recently had a blown passenger head gasket so I took the engine all apart had the heads machined put everything back together (atleast I think I did) and now with the battery hooked up and holding 12.5 V nothing has any power at all, no lights nothing but I can hear the relays clicking on and off constantly. I think it's that I didn't hook up a ground wire, so any ideas at all would be great!!

 

Check grounds to the engine! This is dumb but you hooked up the battery correctly right, seen guys not thinking put cables battery backwards?? My guest is grounds not hooked up.
look around the backside of the engine passenger side. Also do a load test on the battery, Advanced or Autozone will do this for free or recharge it. After a recharge could have 12v but no amps= bad battery

 

The battery worked fine before, and it only sat for 2 weeks, and the battery cables were hooked up right, and I'll have it tested and charges at autozone soon

 

And I'll check my grounds