Hi Kids,
I have an 89 F 150 with a 302. My indash volt gauge would not come up to charging voltage. I checked all the connections, battery and such, and they were fine but no juice. Picked up a rebuilt at the local parts house, simple install, worked for about 5 mins. and then dead. Pull it out, brought it back and said hey, this things no good. No worries, gave me another and off I went. Installed in no time, started the truck same thing. Worked for a bit then quit. Went to the dealer and asked the parts guy his opinion. Said the plug ends should be changed. $45 bucks later, no change. Did notice if I punched the gas, the alternator would come on and work fine untill I shut the truck off and upon restart no juice. Punch it and we're good to go. New battery cables, all new ends, everything soldered and then the brand new alternator ( number 3 ). Doesn't work at all. Put number two back in and as long as I punch it, it kicks on. Help

 

It sounds like the fusible link from the solenoid to the alternator is burnt out. If this is burnt out the alternator won't charge the battery, and the engine runs off the alternator. Running the engine with the battery disconnected using the alternator for power kills the alternator quick. With the engine not running check the black wire with an orange stripe at the alternator for power. You can unplug the harness from the alternator to check this. If there is no power then the fusible link is burnt out or the wire is broken. The fusible links are bolted to the solenoid.

 

sounds like some connection is loose

 

Hi Kids,
Thanks. The cause of the problem was the plug at the back of the voltage gauge in the dash. Power from the ignition but nothing passing to the alternator to tell it to wake up. New plug ( sort of ) and all's well. Always thought the wires that ran to the dash only worked the gauge. Never knew about the ignition feed.
All The Best

 

Thanks for the update, good info.