Conversation Between rla2005 and don1993lightning

Sorry for the long delay in responding but your diagnosis was spot on !
I pulled the instrument cluster and the printed circuit connection (from the exciter to the amp gauge) was quite perished and after cleaning it up to some luster (by lightly buffing) it worked.

The exciter voltage comes through the ignition switch, up into the instrument cluster (Charge Lamp) then continues on to the alternator. Sounds to me you might have a poor connection between the ignition switch and the cluster. Or from the cluster to the alternator. Might be worth a shot to pull the instrument cluster out to check the connectors on the back.

That same 12V from the ignition switch powers a lot of other circuits/devices. If there is no other indication of other devices suffering from low voltage then I would suspect the circuit path to/from the instrument cluster to be the cause.

I need help with my 93 F150 5.8l alternator intermittent charging issue. I installed a brand new Remy 95amp alt (don't know if it's 2G or 3G) , new battery, replaced the pigtail connector, checked all the wiring and ground. Could be the exciter line voltage being below 12 volts(truck has a dash volt gauge). When I run a full 12v jumper wire to the "I" terminal I get a full 14.5v output from the alternator. A mechanic told me to replace the ignition switch (15 pin Ford part #11572) as they sometimes are the problem. Still no output (12 volts at idle). Truck also has Viper Alarm so checked connections to ignition looked OK. For no reason the alternator sometimes runs fine full 14.5v then stops. I thought jiggling the wires around the ignition switch and alarm was the problem but cannot replicate alternator to come on. PLease HELP !!
Truck is all stock Lightning with 90,500 miles excellent condition.