I went to start my truck last night and it wouldn't start, so I took another car out.

I get up this morning and go to try to charge the battery, but it's fully charged (12.5V at all times). Quite literally NOTHING turns on, not even the underhood light. Is there some main fuse that if blown would cut power to everything? The underhood fuse block has power, but still nothing seems to work (Headlights, radio, turn signals, starter)

This is making no sense to me. Can anyone help me, or give me something to try.

I've searched, but I can't seem to find anything that sounds similar.

 

Ok, this makes no sense whatsoever. After making the last post I went back out and continued testing voltages at different points. At one point, I noticed that the underhood light had come back on. Low and behold, everything works again and the truck starts.

I quite literally did nothing of consequence between tests. What gives?

 

To answer your 1st question ( just so you have the info ), there are 2 mega fuses from the battery to the fuse panels

Here is the 1st page of the electrical distribution


Maybe check the battery connections to see if they are loose or corroded ?
Just a SWAG. Depends on what you were testing, and how when there was no power ( don't know how you verified power to the BJB ).

 

I'd start with the negitive cable and then check all grounds. Just a thought!

 

I tested the BJB power by putting one lead of the meter on the negative terminal of the battery and the other lead into one side of an empty fuse socket. It registered 12.5 volts, so I knew it had power.

But checking the grounds makes sense. My meter still would've read having power everywhere (I always left my ground connected to the negative battery terminal) but there wouldn't be any power to start if the ground wire didn't have a clean connection.

Where exactly does the ground wire from the battery go to?

 

Look in the reply from sscully, he's the electrical guru. Also check the resistance in the ground/ negitive cables.
Good luck and post your results.

 

Next time it fails, connect your voltmeter between the engine block and the negative battery terminal. A good ground cable with secure connections on both ends will show little to no voltage across the 2 or 4 ga cable. A bad cable will show a voltage anywhere up to the battery voltage across the ground cable.

The ground cable usually gets attached to one of the starter mounting bolts. Inspect the insulation and look for any bubbling from inside the sheath.

 

not sure but at the battery isnt there a second positive cable with a quick connect attached to it maybe the quick connect is a little loose I think it brings power to the relay on the fire wall then to starter.