Ok. So I am in need of help again. I have an 89 montero 2wd/4wd auto 6g72. The problem this time is the battery won't seem to charge. It is a brand new battery, and checks out as good. The alternator is rebuilt by me, and has checked out as good as well by checkers and autozone both a few different times. I put a new ground, and even another hot wire to the battery. I have been looking into how the alternator works, and every thing would point to the battery charge light, as if it was out it would not charge the battery. The truck runs fine so long as the battery has juice, and runs fine under its own power, as long as the battery is not connected. But in about two days it will be dead. I recharge them and I am good to go. This is my third battery, as the vehicle fried the last two. Every one I have taken the alternator to has said not to waste my money. That I did a great job rebuilding it and it has the correct amps and volts as it should. Any help would be great.

 

check the 90 amp alt fuse on the battery cable like your manual says

 

At night, connect the battery. Next day before turning on the engine, touch the alternator, if it is warm, the bridge diodes inside it are shorted and needs replacement. In other words, alternator is bad, you may have it repaired again or buy a lifetime warranty alternator and everytime it goes bad, change it free of charge.

If you like testing, you may perform a simple test with a multimeter. Take out the negative terminal cable of the battery. Have one test probe connected to the terminal cable and the other to the test probe to any metal part to complete the circuit. Have the multitester in the milliamp setting. It should not draw more than 40-50mA. If it goes more than that, something is bad, current is shorting to ground and draining your battery slowly. It happend in my case. I did this test and had a current drawing of 800mA, almost 1 amp, it was the alternator leaking current to ground. Remember, to do this test engine must be off with no accesory turned on, no key on the switch.

 

@redcentinela thanks I will try that. I really like my truck and want to keep it. I have put so much time and work into it.
@mxmikie thanks but no thanks. Sorry I forgot to say I have good fuses. I know I am new to the forum, but not new to working on cars. And yes I have a manual. And it is junk for what I have fixed on this truck.

 

Just keep us informed about your findings. According with what you say that your battery last about two days, for sure there is current leaking to ground and the most provable problem is alternator"s leaking diodes to ground. If not, you will have to verify all the cabling in your truck. There must be a short somewhere. Good luck.

 

@redcentinela
So it has been a few days. And hot here in vegas, so has been hard to tell by touching it. Did a read and it was 48mA. Truck has not gone dead. Whatever this is seems to come and go. But the funny part is the truck was acting up 2 of the times I had it tested. I don't know what to do. I may just buy a new alt.

 

It is easy. First thing to do is to touch the engine, then the alternator just to compare temperatures. Temperature at the engine bay should be the same. If alternator is warmer than the engine, then alternator is bad. If not, something else must be wrong. 48mA is not bad. Those amps are usually used by the vehicule's computer. Verify all the grounds just in case.