Battery not charging.

[NEALD]

I've recently found that my charging system is not working properly on my 89 bronco II. The previous owner said the alternator was new but I had it tested anyway at local AutoZone good. I then tested continuity and voltage for power at alternator BK/OR and YL/WH wires. Good also. I cleaned and inspected negative cable and positive cable and their respective connection ends. Still no charging. Battery is charged, started at 12.7v, after starting and running the vehicle for 10 mins the battery was down to 12.3v while still running. Could alternator having a bad ground and a poor body ground do this?

 

[JerryC]

When you took the alt off how did the mating surfaces look?

If the ground is good enough to start the motor then i would think the battery to motor ground path is good enough.

Check for voltage at the wire from the alt to the battery.

I haven't seen a 89, but I've read that connector for the wiring harness at the alternator is prone to overheat and may need to be replaced at times.

 

[NEALD]

I removed the alternator and cleaned mating surface and attachment bolts. I also installed new grounds to body, alternator, engine, and chassis. I cleaned alternator spades and their respective connector, along with measuring the exact same voltage at BK/OR and YW/WH power wires at alternator. I don't seem to have any draw at battery key on engine off, or key off engine off. In fact I can charge the battery to 12.7 volts and leave it for a week hooked up to the vehicle and the battery is within .02 when I go back to it. Before I start the vehicle battery is at 12.7, after cranking and starting the engine cold it come down to about 12.28 and drops about .01v about every 4-5 seconds. Im thinking AutoZone may be wrong. I have a 3g alt in the shed I may convert to.

 

[3rd Petal]

It wouldn't hurt to buy another alternator and put it on to see if it fixes it. If not then return it. But I have worked on a f350 in the past that was at a big shop here in Reno for a few weeks with a charging issue, and they messed with it for a while, ended up putting 2 different new alternators on it, and it still wouldn't charge so they gave up. Then the owner of the truck came to me, and I put a new alternator on it and poof, it was fixed. So the shop got 2 brand new alternators in a row that were both no good. So keep in mind it could be something as stupid simple as that

 

[Jim Oaks]

Here's some info on checking the charging system:

http://therangerstation.com/tech_library/chargingsystem.shtml

You haven't removed and amp or voltage gauge have you?

 

[NEALD]

Some good info there. I will try those tests in the article. No. I haven't removed anything from this vehicle. Then again this doesn't mean the previous owners didn't. I bought the vehicle not running, replaced the tank and fuel pump and this is where I am now. How do I tell the difference if I have an ammeter model or not? I know I have a volt meter and a alternator light, is there anything else? Maybe I will check the owners manual to see if its in there.

 

[NEALD]

Conclusion.... Alternator is bad. Thanks for all the helpful info guys. On to the next project.

 

[Jim Oaks]

As long as it doesn't look like someone removed the amp gauge or voltage gauge (which ever it was equipped with). They actually feed voltage to the charging system which 'excites' the charging systems and causes it to start charging. It would only be a problem if someone had removed those and cut the wire.

 

[NEALD]

Not sure if anything was cut. I do know that with the old alternator I had an alternator light illuminated and the volt gauge needle was between the 8 and 12. Now I have no alternator light and the volt meter reads a quarter inch above the 12. I also measured voltage over 14.1 at battery within a minute of running, before it was 12.2 and dropping after start.