ok, so I got a 89 pickup, 22re manual trans. so ive got a parasitic drain when the truck is off. right around 2.8 ma. did the the pull the fuses to find out what it is that is pulling the extra power and the charging system is the culprit. well I had extra alternators laying around, mind you they are a little used and abused just by looking at them. so I had it tested and it tested good, swapped it out, and the drain dropped. originally it was 3.8 ma. so now I'm down to the 2.6-2.8 ma. still enough to kill my battery in a few days. so somewhere in my alternator system is a short and something that isn't operating right, and I'm just at a loss at this point. so far due to other things going out, I have a new optima red, new alternator(buddy warrantied one for me), new ignition switch, traced out the harness from the alternator to the drivers side fender, and rebuilt it. was looking rather poor. so where to go from here? I have a vm, and a fsm with a schematic, but with the truck off, what can I test from here to try and locate this little bugger?

the new alternator charges like a champ. even the old ones did their job well. But after a few days, the battery would lose enough juice to be able to start without help. if I drove the truck everyday and a lot, I wouldn't have any issues. maybe the occasional dead morning battery. so ahead of time thanks for your help.

 

I have cured those drains from Just upgrading all the ground cables on several vehicles


Is it possible that you might have the glove compartment light on .

A corroded connection that is just enough of a short to drain the battery but not melt wires or open circuit protection.

The alternator plug comes to mind .

Your battery is clean ??

Terminals clean and tight ??

Added after market device drawing current . Cheap China built chargers drawing current all the time when plugged in??

Just how did you figure it is the charging circuit what did you remove ??

This might help narrow it down to some other circuit

As the Terminal B of the Alternator is connected to the fuse block .

 

New battery, new terminals. Located it to the alternator or something to do with the alternator by removing the AM fuse. I forget whether it was one or two, but it was the one for the alternator. So, if u unplug anything from the alternator, the power draw goes away. New alternator. Had same power draw with two other ones installed. Grounds are good. And no after market accessories.

The drain is alternator related. Just lost as to, how do I test and find it it from here. I can here a small faint amount of current running through the alternator, a small buzz or whine. Very very faint, but it stops once fuse is pulled or unplug the alternator.

So that's what has me thinking that something in the alternator system isn't functioning right, cuz is running current through the alternator, but new alternator, and wire harness rebuilt at the alternator.

So what else is left? Switch? Relay? Dash light? This is where the fsm gets vague.

 

That is where you are misleading yourself

Both the AM 1 and 2 fusible links carry current to many more circuits then just the alternator

Does your current draw only go away when the alternator is completely unplugged both the 3 conductor plug and the B terminal lug unbolted.disconnect the negative cable or you get some interesting results insulate the bare end hook things up to test

If that is the case most likely a Shorted diode allowing the current draw .

This draw would be so small it would most likely slip through QC

 

Ok. So unplug am1, current goes from .286 down to .007. B+ terminal on alternator takes it down from the .286 to .031. Unplug the harness from the alternator it drops to .007. These were all done separately.

Mind you this is a "new" alternator. I'd like to test all other options before thinking it's the diodes again. The first alt I changed had bad diodes. It's draw was massive. But I'm getting nearly identical power draw numbers with 3 different alt.

Again thanks for the Input. I need some fresh perspective on this problem.

 

Well, this means that I am not crazy. I too have a similar drain issue. I unplug the alternator and the drain goes way but I just couldn't wrap my head around it being the alternator. Alas, I just haven't had the time to really troubleshoot this issue. I can't remember what my draw numbers were but my battery would be DEAD within a few weeks. So, I just plug the battery into a solar panel regulated charger to maintain it lol.

Anywho, good luck with your troubleshooting as I hope you figure it out!

 

Well, rethinking the numbers I'm getting with each individual component unplugged, I'm kinda leaning towards my new alternator having a bad diode.

Unless someone chimes in saying to check component "x" cause it controls this thingy on the alternator, and when it fails it won't shut the alternator off.

 

I also found a video on a diode check. Basically set vm to diode check and touch post b+ and the case. But without specs to verify my findings it's kinda a stab in the dark.

 

Interesting. There has to be specs around here somewhere .

 

Specs on output are easily available. Can't find much on diode testing specs or anything really outside output.

 

Well, hopefully someone can chime in .

 

Not trying to be smart here just curious .

Do you understand how diodes work ??

They allow current to flow in one direction only!!

They can work

They can be shorted allowing current to flow in the opposite direction or to ground.

This can be detected with your meter

They can be open meaning nothing flows through them

No real specs to test .

So the 8 diodes in the rectifier one could be shorted and the alternator might still have output.

these things can happen in any number of ways so really no hard fast rules

Something like this would not be picked up by a load test

Installing alternators with a discharged battery can cause diode problems

 

I did the diode test that I found on the old interweb and basically you place one test probe on the b+ and one on the case of the alternator. Then switch probes. High reading one way and a low reading the other way. Where I would like specs on that is should one way be 0, no reading, hence all the diodes are good and if I do get a reading that means 1 or more of the diodes are bad allowing back flow.

That would make sense to me, just looking for a little verification somewhere, before I pull it out again and take it back to oreilley. They are sick of seeing my face.

 

A forward-biased diode has a voltage drop of 0.5-0.8 volts (these are silicon diodes; specialty germanium diodes have a lower forward drop). Reverse biased, as long as the voltage is below the PIV (Peak Inverse Voltage), essentially no current will flow. (The PIV for these diodes is probably around 100v).

With the "diode test" function of your multimeter, the multimeter provides a small CONSTANT current (the same constant current it uses to measure resistance) through the diode, and measures the voltage drop. When forward biased, it should read 0.5-0.8 volts. Reverse biased, it should read something like 0L (overload, or overrange), telling you it can't push even that small current through. http://en-us.fluke.com/training/trai...ultimeter.html

That's pretty much all you can test. From B+ to case, you're measuring 8 diodes, 4 series-pairs in parallel. So the voltage drop you measure should be 1.0-1.6v. The trouble is that if only one of the diodes is bad you won't be able to pick it out.

So take the alternator apart http://web.archive.org/web/201102051.../3generato.pdf and test the diodes one at a time (the manual shows testing with an ohmmeter, which is good enough, but you have a diode test function, which is better.)

Last, there is no such thing as "no reading" from a multimeter. "Zero", whether volts, amperes, ohms, or something else, is absolutely a "reading."