Electrical cuts out when attempting to crank

2000 XLT F150 4.6 - New starter & solenoid(s), battery cable & fuse links good.

All electrical appears to be good. Then when I turn the key, I hear a single click and the power cuts out entirely. I can't attempt a second start or turn on the lights or have any power going through the truck until I disconnect the battery for about 10 seconds then reconnect. Electrical becomes live again, then when the ignition is turned the electrical cuts out again. I do hear a single click at the starter (probably attempting to engage when the electrical cuts out) and a clunk right at the inside fuse box (drivers side). Anyone come across this before?

 

Bad battery, bad battery cable, bad ground at starter.

 

Or the relay on the firewall is connected wrong. (Some call it a solenoid)

 

Clean the outside of the battery posts and the inside of the cables that hook onto the battery posts. Make sure the cables tighten up properly when reinstalling. That usually fixes the problem you are having.