My truck lost all power while driving on the highway yesterday. I was stranded away from home for 3 hours

I charged my battery last night and today, I tested everything except the mega fuse. I can't find the damn thing!!!!

I think it's the alternator giving me issues, but based on everything I've found on this site, the mega fuse MIGHT be the culprit as well.

My truck is an '04 4.0L V6. Can anyone post a picture of where the mega fuse is? It's the 175A fuse that prevents power from going from the alternator to the rest of the truck.

Thanks.

 

Never heard of a mega fuse.. but if I had to guess. it'd be under the hood somewhere. Got a manual? Test the alternator?

 

Get a Volt meter, set it for 20vDC

key off, engine off
Touch Black probe to "-"(Negative) on battery
Touch red probe to "B+" on the back of the alternator(it is the big terminal with the big wire and nut)
If it shows battery voltage(12volts) the "mega fuse" is fine.

Follow the B+ wire it goes directly to the mega fuse, usually located next to the Power Box in the engine bay.

Vehicle can continue to run just on battery power, with headlights on about 20 minutes, headlights off 40 minutes.
And it won't just shut down, it will start to run rough as spark voltage drops and then die as spark and fuel pump stop.

So there would be no sudden shutdown.

Battery voltage should be 12.3 to 12.7 volts
With engine running battery voltage will show 13.5 to 14.8 volts, the extra voltage is the alternator working.
4 to 5 minutes after startup battery voltage should be down to 13.5 to 13.7 volts, that's the maintenance charge to keep battery charged but not boiling, continuous voltage above 13.9 volts will ruin battery over time.

 

Bad alternator...

I had already tested the voltage yesterday morning (forgot to mention that). It only registered 11-12 volts with the engine running, but I had read that if the mega fuse is bad, it would prevent the battery from charging too...

...but then again, it would also prevent ANY power reaching the vehicle's other systems.

5 minutes to remove the alternator
1.5 hours to go had the alternator tested and buy a new one
5 minutes to install the new alternator

lmao

 

Good work

 

1. I just had a similar problem , 94 ranger kept blowing alternator fuse. Started gradually then blew every time I started it. I checked the yellow and white wire for , it was fine along with the black and orange with the linked fuse that was fine also. I checked everything I read about and what it ended up being was the ground wire coming off the starter had come loose from under the heat shrink tape and was shorting our cause too much amperage to go to fuse box. I’m only writing this because none of the forums told me to check starter wires. As it does not seem like a starter issue cause it starts fine but would blow the fuse. I checked every dang wire on my truck I ine paper and rewrapped them all. Changed the inline fuse, checked everything, wasted my whole Sunday for a shorted starter wire. Hope this helps someone