Where is the Mega fuse located on a 2004 Lincoln Navigator

check the wiring and connections to and from battery

Some thing wrong with charging system. Need to check under hood. Could be belt, alternator, or battery issue. Require a voltmeter, should be somewhere in the area of 13.8 - 14.5 volts when engine running

battery draining at rest. check for drain turn off all accessories. disconnect ground. attach a testlight in the bridge between battery and ground cable. if the test light glows start removing fuses one at a time until the light goes off. replace each fuse that doesnt quelch light immediately. when you quelch the light you have a circuit to inspect thsat is draining the battery

If the thick black and orange wire does not have battery voltage, there is a fuseable link near the battery or starter that is melted.
Same thing with the smaller orange and lite blue wire.
The smaller wires involve the computer and the instrument panel warning light.

Did you check for B+ voltage at the heavier gage wire on the back of the alternator ? When yor turn the key to run , not start , does the charge indicator light ? When the vehicle is running is that charge light lit or off ? There is a fuse that supplies B+ voltage to it . Fuse # 30 located in the central junction box , it's a 30 amp fuse ! Plus one more fuse located in the battery junction block # 11 20amp . With out B+ voltage at these connections on the alternator it will not charge .

This light means that most likely your alternator has stopped functioning, and your battery is no longer being charged. Typically this means that your alternator needs to be replaced.

This light is not like a service light, you still have a problem, and it appears that the alternator was not the issue. I reccomend getting it diagnosed, but do look for grounding issues, and clean battery terminals.

alternator is not charging the battery. have alternator checked and replace if bad.

have your battery and alternator tested. sounds like battery. No need to replace cable unless it is frayed or in poor conditin.

you should have 12 volts at battery with engine off.
should have about 14 volts if charging.
what are you getting?

check fuse 20 in power distribution box on left side of engine compartment.