2013 TRD off road, charging trouble - SOLVED

I've got a battery that takes a charge off the charger, but not from the alternator, the voltage at the battery is in the 12v range, and 15V on the alternator post.

I've checked Alt-S and IG1 #2, and those two are OK.

I'm trying to pull the 140 amp alternator fuse, but it doesn't seem to want to come out. I've pulled on it till I think the plastic is going to break, but it doesn't come loose. Is there some trick to get it to come out?

 

The main ALT fuse is bolted in at the bottom of the fuse box, you have to pull the box up and get the bottom cover off to change it. It's not easy or fun to do.

Pretty easy to tell if the fuse is good, key on engine off see if the brake lights work. If they do then the main fuse isn't blown.

If the fuse is good then it sounds like you have a voltage drop on the main wire from the alternator to the underhood fuse box, most likely at one end or the other either in the crimp or on the ring terminal.

 

Key on, Engine not running and the brake lights work as normal.

I guess my next step is to check continuity from the alternator top post to the positive battery terminal.

 

Continuity may test good, I'd check voltage drop.

Engine running, meter set to volts DC, one lead to battery positive and the other to the stud at the alternator, should be less than 0.5v.

Same check from the negative battery post to the alternator case.

 

More than 3V difference.

I have no continuity, open circuit, from alternator top post to positive battery terminal, so I think it has to be the wire from the alternator to the fuse box or the fuse box to the battery, so I have to disassemble the fuse box anyway.

I worked at pulling the insert out of the fuse box for half an hour, but, as you stated, that isn't fun.

 

What's the wire look like at the alternator and battery cables?
Got any pictures?

Would be pretty unusual for it to be bad in the fuse box.

 

Everything under the hood looks good, no corrosion, no loose (from pulling on things) wires. The battery terminals are corrosion free.

I'll grab a few shots and post them.

 

Also was the 3v on the power or ground side?

 

3V is from 12ish on the battery to 15 ish on the alternator when running.

Testing continuity from the + battery connector to the alternator top post with the battery out is open circuit.

 

I'd bet money your problem is right there, it's obviously been hot which is a telltale sign of a poor connection.

 

That was it, took it off, cleaned and reinstalled. Truck is back up and charging normally.

Frankly I hadn't had a good look at it till I posted the picture, and the same thought occurred that it had been hot.

Thanks for your help!

 

Glad to help and it was an easy fix.

You might add (Fixed) or (Solved) to your title so others may find this helpful.

 

Will do, thanks again!