1999 F150XLT SC, 5.4L, 100,000 miles, PW, PL, AC

I just replaced the alternator (100% new from O'Reily), new Optima red top battery, new Gatorback serpentine belt. Everything went together beautifully thanks to the great instructions found in the forums. When I connected the battery cables there was no electrical power (no courtesy lights, radio, nothing). About 15 minutes after connecting the battery the courtesy light under the hood lighted and all was well, the truck started and ran great, 14.4volts at the battery.

A couple of days later when I turned off the truck the same thing happened, it lost all electrical power for about 10 min. Checked all fuses, ground cables, battery volts. When the power returned I started and checked the volts at the battery... 14.4volts. All windows, AC blower, radio worked as they should.

Today I had the same problem, the truck started and ran great... stopped at the store, turned off the engine and no electrical power. This time I hooked up my DVM to check the battery (12.7v) also checked volts at starter solenoid, also 12.7v. After about 10min. (while checking volts) the courtesy light lighted and the truck started and ran fine.

I've driven the truck during the day and at night since replacing the Alt and Bat. While running I haven't experienced any electrical problems.

A few other notes: The windshield was replaced/resealed at about 1yr old and there are no signs of water on GEM or either fuse box. The only intermittent problem I'm aware of is the common odometer issue.

Can anyone suggest what to look for?

Thanks

 

You COULD have a faulty ground connection from the battery to the frame or engine block (I don't know how yours is connected). This seems to be my favorite "diagnosis", because I've seen it more than once on older vehicles.

It would be easy to check though, the next time it happens (if you have your voltmeter). Touch the positive probe to the positive battery terminal. Touch the negative lead of the DVM to a clean metal part of the frame, like a bolt somewhere in the engine bay, not the negative battery terminal. If you read battery voltage, my diagnosis is WRONG. But if there's no voltage, that's the problem.

It might be a bad connection that's aggravated by heat. Once your truck is running, it's being powered by the alternator, so a poor ground would not cause failure, but - the battery acts as a "buffer" to prevent alternator voltage fluctuations. If the battery is out of the circuit, you are sending some fairly damaging voltage spikes to the electronics.

- Jack

 

Jack,

Thank you for replying. The problem hasn't occurred again, but I've tried to do a little prep based on your reply. I located a few ground connections at the firewall and was able to read battery voltage at each point by connecting the Positive lead of my DVM to the pos lead of the battery an then touching each ground point with the neg lead; all read battery voltage. Just in case some resistance was building due to heat I removed cleaned and reattached each ground. Additionally, I took a few voltage readings at the fuse boxes with the truck off in case it happens again I can see if electrical power is reaching the fuses.

I noticed something else that may or may not be related to the problem. When turning the ignition to start the truck the interior lights turn off completely while the starter is cranking. In fact, I have a Sony stereo with a hard drive that starting doing a file check each time I start the truck indicating it was loosing all power (the Sony has been in the truck for 7 years and was installed using a harness the plugged into the factory stereo connector so no wires were cut or spliced.

Could this be a problem with the ignition switch? I don't have schematics so I'm working a little more than blind.

Thanks again,
Mark