No start, no crank; battery good. 93TBird

Car ran just fine until this morning. Just returned from a 500 miles trip with no problems. Now, when I turn ignition switch to start car, there is one loud click then all power is lost (no lights, NOTHING). About 5 minutes later power returns. Same thing happens if I try to turn on headlights. Interior lights and radio work fine. Checked battery and battery connections - all are fine and fully charged. Connected car to a new battery, same result. Hooked car up to another running car with jumper cables, same result. All fuses are fine. What could cause this? starter selenoid? short? bad relay switch? Is there a capacitor that could be faulty? Thanks for any help!

5/25 update: I verified that juice is getting to starter. Replaced starter as it tested bad. However, still no crank: 1 click then all power is lost for several minutes, then it returns - only to repeat if I try to start the car again. Bad relay?? This has me stumped ...

Possibly a short around the starter. Thats my first thought but I realy am not sure.

Sounds like a loose connection. Start by checking all the connections one the solenoid, starter and all grounds..

check to make sure that the battery is seated correctly and secure. I have a '94 and something similar happened to ours. The battery was not completely secure and had moved slightly forward and was grounding out on the chassis. We just slid it back and it was fine. Good luck. Schellie

Try taking the bat cables off and seeing if there is any corrosion inside the terminals, these cars seem to be super sesitive to the battery and its cables. This caused this exact problem on my bird.

personnally i ussualy advocate getting a pro to look at it. my boss puts it best when customers guess whats wrong and dont let us look for ourselves. " we should make a dart board, and label car parts on it... we fix/replace what they hit... if it doesnt fix the problem... throw another dart" basically what im getting at is make sure everything is workin. but basic questions : how did you check the battery? (<tool, "charging system tool" <checks for drains, and alternator amps, ect) are all connections tight? because if you have luck like me thats all it is. i had the same problem with my cougar.. i cleaned the terminals, checked every damn thing... the battery was toast. but ive also had the new battery in and because of a loose connection (ussualy either the pos or neg) it vibrated loose and wasnt getting enough contact)

I have the same issues.... did you find out what caused the problem? replaced relay and????????? i give up.HELP