I was driving my 98 F150 5.4L home last night and the lights were getting dim then the radio went out then all the gages including the speedo went out and by the time I limped it home I had no power, it was sputtering and died. I figured it was the alternator so I pulled it and had it tested and it was good. Any ideas on what it could be???? Any help would be appreciated.

 

Well, for whatever reason, the alternator output wasn't reaching the battery so your battery is now COMPLETELY dead. Put it on a charger (do NOT attempt to recharge it with an alternator) and fully charge it.

The output of the alternator goes to the 175 A megafuse on the firewall (under the cover next to the starter relay). Check that fuse. Also there is a 20A inline fuse that goes between the same connection at the megafuse back to the alternator that controls the field current. Check it also.

Steve

 

check everything he said along with all batterty connections,grounds etc..make sure your belt tension is good also

 

I have the same probelm, but I can't find the megafuse. I have read several post describing where it is, but I can't locate mine. It is a 1999 V6. Anybody got a picture showing the location?

I followed the cable from my alternator to my solenoid, but did not see the fuse.
I think I am losing my mind.

 

It's under the plastic cover on the firewall along with the starter relay, near the battery.