Sorry if this issue has been covered, I could not find a solution for the problem I am experiencing no matter what key words I've used while searching.

Here is the story . . . 1999 F150 w/ 5.4L & auto trans, 206k mostly trouble free miles.

While hauling some pavers home from the local store I decided to stop to give the truck a break after pulling a couple miles of steep road up out of a river canyon, even though it showed no indication of overheating or anything else unusual.

Stopped at an abandoned restaurant and parked in the shade turned engine off. Decided there was a better spot, started truck, relocated and shut it off. Sat about 20 minutes and was ready to move on. Keyed it and all I got was clicking from the firewall mounted starter relay.

Sat there with the hood open and let it cool more hoping it was just a heat issue. Waited a half hour and tried again, got a battery light and gauge sweep on the instrument cluster, same clicking starter relay on the firewall and no starter actuation.

Called for a tow truck since I had no jumper cables and there was nobody around to try and get a jump from anyway. Tow dude shows up, grabs his portable jump box, hooks it up, keyed it and fired right up. Let it run while filling out the paperwork and drove the last 30 miles home with no issue, parked in my driveway. Shut it off and tried to start it . . . click-click-click!

Grabbed my big Optima Blue Top Deep Cycle trolling motor battery, jumper cables and hooked up . . . vroom started right up.

What I’ve done since:

- Installed a working battery from another rig. NO GO!

- Put F150 battery in donor vehicle. WORKED FINE!

Note: Any battery connected to this pig whether in a test start or jump start configuration is rapidly pulled down from an attempted (no jump click-click) or successful (jump and starts) test.

- Installed new OEM starter/solenoid (not reman), cleaned ALL connections between it and the battery. NO GO!

- Installed new OEM firewall starter relay. NO GO!

- Replaced alternator with new OEM replacement (not reman) even though the output from the original alt read 14.7 at the battery, tossed a new serpentine belt on while I was in there. Reason being, my ’05 Mustang GT lost an alt diode, was throwing codes indicating same, still showed normal output on a VOM but was not properly charging the battery, so I figured what the heck. NO GO!

As of now the only thing I have not yet done (that comes to mind) is to disconnect the hot lead from the firewall mounted starter relay to the starter solenoid at both ends and read end-to-end continuity and end-to-chassis ground, as I suspect a short somewhere in that run.

I’d really appreciate some other suggestions at this point since my mind started to fry long ago.

Thanks . . . Bob