Weird Charging/Alternator Problem

[RiggerRob]

Hey, everybody,

I am encountering a head-scratcher with the charging circuit in my '84 Tercel wagon. Up until about 2 weeks ago I wasn't having any problems and then suddenly I noticed the light on my 12v accessory panel was flashing (this happens when the voltage is low). Next thing I know, my battery isn't charging and I'm getting my roommate to jump me to get to work. I got downtown and the car dies in the middle of an intersection - luckily I was able to get out of the street to a safe place. I called my roommate to come down and get me and she was able to jump the car and get it started again. I checked the alternator output voltage - it seemed kind of low at the battery terminals, but I was able to lift the negative battery terminal and the car kept running (although the alternator output seemed pretty erratic) so I assumed (yeah, I know, bad word) that the battery was shot, being a 4 year old Walmart battery and all. I went to O'Reilly's, had a new battery installed and went on my way. Up to this point in time, the charge or brake lights never came on during the entire ordeal.

The next day I came out to my car to discover the battery was dead. I went ahead and ordered another alternator (the internal regulator type), picked it up a couple of days later and installed it. At this time, the charge and brake lights came on and stayed on. The guy at O'Reilly's tested it in the car and we determined that the regulator output was low. I ordered another alternator thinking that I had a bad one from the warehouse. We installed it today - same symptoms. We pulled both alternators and bench tested them at the parts place and they both read 14.4V on the tester. The voltage in the car is only 12.9V and doesn't seem to go up when I rev the engine. It pulls down as low as 11.8V when the A/C, fans and lights are all going.

The other really weird thing is that now the engine dies when I pull the negative battery terminal, which it didn't do when I tested it with the old, original factory installed alternator with 237,000 miles on it. I also realize - in hindsight, of course - that I should have had the old alternator bench tested before I did anything else. I have tried directly bypassing the hot lead from the alternator to the positive battery terminal, which seems to make no difference. I have also checked the 7.5A 'charge' fuse, which seems to be fine, but if I am reading the electrical diagrams right, this fuse should have 12V on it when the car is running and is directly in line with the brake and charge lamps. This voltage should be coming from the 'L' pin of the 3 prong plastic plug in the back of the alternator and should make the charge light go out when active (I haven't had a chance to thoroughly test it because it's already dark here).

I've searched the forums for similar problems and the nearest possibility I can think of is a faulty ground problem, although I also saw that ignition problems might cause this (Teddy does a great job of listing the possibilities here). I have not replaced the main ground lead to the battery yet, which is my next troubleshooting step. The two things that are mystifying to me are the engine dying when I pull the battery terminal, and the lack of voltage on the 7.5A 'charge' fuse. It seems pretty likely that a wiring problem is the issue here, but any experience you guys could share with me to give me a boost in figuring this out would be greatly appreciated. Sorry for the lengthy post here but I wanted to make sure I had covered everything.

Thanks in advance,

Rob

[dlb]

shouldn't a running car normally die if you remove either of the battery terminals? you're breaking the circuit then. i must be out to lunch. time for david to learn something.

alternator was my first guess since the car died while driving as opposed to drove fine but wouldn't start, which is usually a bad battery. i think we can rule out those two though. the fact that the car suddenly started acting up suggests that something must have changed. did you do any work on the car recently involved the electrical system? i once grounded out the hot lead to the electric carb choke and that lit up some idiot lights so check all your fuses in all three locations. i would also check all the green and white plugs by the battery and make sure they're all connected and the grounds to make sure they're not corroded or super dirty.

[xirdneh]

i have driven several cars short distances with the battery removed "after" engine is running.
but recently found out its not a good idea
i hear the alternator output increases dramatically when the battery is out (thinks it needs to charge something)
and the extra output can damage electrical components
i know this may be true for modern cars but wonder if older cars are immune?

note: i hear you cannot push/compression start a car without a battery
because the alternator needs at least a little bit of juice to get going

[Petros]

the car will run without a batter if the alternator and regulator is working properly. You need a small amount of battery power to push start a car or you will get no spark.

I would check all of your ground contacts, at battery, at engine, head and at starter. Also, there is a relay and possibly a fuse for the alternator, check your fuse panel, both the one under the hood and the one under the dash (I seem to remember it being in the one under the hood). Possible you blew the fuse when you ran it without the battery in place.

[RiggerRob]

Thanks, guys, I think this all looks like grounding/wiring issues. I regret not testing my original alternator in the first place but at least when I nail this down I'll have a new alternator and battery in place. My next step, after talking with my mechanic, will be to replace both the negative and positive leads on the battery right back to the engine block and chassis. One interesting thing he said is that on older cars, corrosion can actually creep all the way up the cables inside the insulation where you can't see it. He says that he's seen guys replace four starter motors on a truck before they finally realized it was an intermittent ground cable. I've got nothing to lose when replacement cables only cost about 8 bucks apiece. Thanks for the help, I'll keep you posted.

[RiggerRob]

UPDATE: I figure all you guys would need a good laugh so you can have one at my expense.

I got on the phone with my mechanic and we talked through the problems I was having and I mentioned in passing the big square black box by the battery which happens to say VOLTAGE REGULATOR on it. All this time I had been installing an alternator with an internal regulator on it, so I was basically scrambling my poor little Tercel's electrical brains! O'Reillys was nice enough to refund me for the internal regulator alternator and give me the core price back on the new one (which is considerably less expensive). I also got a good blissing out from my mechanic, who I profusely thanked for helping me extract my head from my *ss.

Of course, when I installed the new alternator everything worked just fine (fortunately, I didn't fry my regulator or any of the other wiring in my car). I'm also much more intimately familiar with the electrical and charging system of my Terc. I guess all's well that ends well and I didn't lose a bunch of money or trash my car but I'm certainly gonna pay a little closer attention to what I'm doing from now on...

[dlb]

ha! whatever, live and learn. there's a saying, something like "wisdom comes from learning which comes from making mistakes which comes from a lack of wisdom..." so now you know and are that much more wiser!

[Petros]

the alternator connector is different for these two alternator (internal vs. external v/r), so how did you manage to connect the wrong alternator to your car? You must of worked hard to accomplish that.

[4wdchico]

i have driven several cars short distances with the battery removed "after" engine is running.
but recently found out its not a good idea
i hear the alternator output increases dramatically when the battery is out (thinks it needs to charge something)
and the extra output can damage electrical components
i know this may be true for modern cars but wonder if older cars are immune?

note: i hear you cannot push/compression start a car without a battery
because the alternator needs at least a little bit of juice to get going

You are correct about it not being a good idea to drive w/o a battery in the car. Without the damping effect that a battery has on voltage swings, components can be damaged. In an emergency, sure I would drive w/o a battery, but I would be prepared to suck it up and deal with any issues caused by doing so. I would just take the positive thinking path and rationalize that any component that failed was on it's way out anyway...

[RiggerRob]

Petros,

The connectors must be pretty close because I was able to get it on. I did have to push it on pretty hard but didn't feel like I was forcing it.