First time posting here. I have a 1999 Montero Sport and it is having the following issues:

* The alternator does not always charge the battery fully even on long rides.
* Alternator was checked and found good, same with the battery.
* When the weather is cold it seems to charge fine.
* When the weather is above the 80's it does not charge consistently and has issues starting.
* The issue is when trying to start, the battery is really low and it's a pain to turn over with clicking, etc.
* A few times I thought it was dead (no lights, nothing), but when I opened the hood, the alarm went on and off, I pressed lightly on the engine fuse box and the alarm was screaming at me. And then the truck started fine.

I believe there is a bad connection between the battery/fuse box/alternator. I don't know where to start with this. Any suggestions? Thanks!

 

well, id start with the connections between the battery/fuse box/alternator.

Something hasnt been tested correctly.

 

First off a disclaimer: I don't own a Montero at the moment. I'm just lurking around to learn from you guys. BUT, I've owned a bunch of other rigs. Here are two things I would inspect:

1) I bought a Land Rover once that had the wierdest charging issue that sounded very similar to yours. Turned out that it is possible to route the serpentine belt in an orientation slightly different than the 'right' way. The belt in the 'wrong' orientation has a pretty good amount of tension but not quite ENOUGH tension. The pulley will slip when too much load is put on the alternator (A/C, headlights, etc). Therefore in hot weather and at night is when I had problems. Of course, I didn't notice it until the next morning and thought it was discharging. The lack of charging was a lot worse at highway speeds. But if I drove around town it would charge enough to get enough juice in the battery to start back up. On highway drives when the alternator would slip more, it would sometimes also make my dash lights flash in a crazy manor making it seem like a voltage regulator or wiring. The previous owner's mechanics couldn't figure it out and some mechanic/s tore the dash apart looking for the problem ..and supposedly really pulled their hair out. So, it's worth double-checking the belt routing. On my yr land rover there wasn't a belt routing sticker that most vehicles have, and when putting on the belt, whoever installed it put it on in a manor that at first glance is how most people would probably do it. The 'right' way is a pretty unintuitive path. Not all vehicles have belt routing stickers.

2) Tension and pulley - Look closely at the pulley. Look for glazing and/or sharp ribs. It could be the tensioner not doing it's job, or belt glazed. Have you replaced your belt?