Engine that's been sitting

[mtrans]

If battery is bad you can get this.Try with some that is good you must have more than 13,7V.

[RunninWild]

Its a brand new battery. It's turning the starter quite well. The charge is starting to get low on it though.

Even if the battery is practically dead it should still put out over 13v at idle shouldn't it?

I think I just killed the used alternator I bought today. When I unhook the positive lead the engine dies instantly now. I new pulling the lead was hard on it but didn't expect it to *** the bed so easily lol.

I also just tried bypassing my factory harness and hooking the alternator up to the battery with jumper cables. With no luck. This just doesn't make sense...

[ORCoaster]

What kind of ground condition do you have for the battery and the engine?  Almost sounds like something amiss there or in the voltage regulator.  I have a new regulator that I bought but then my son gave me a new alternator about the same time as it didn't fit his Dasher. 

Send a PM if you want it. 
Just need an address to send it to.

[air-cooled or diesel]

if battery is good, id start with the grounds, cleaning up grounds and adding more can help. also clean up pos side, maybe a new charging wire/or wires. taking off pos strap with motor running is a hard time for the alt. the charge has nowhere to go, as the battery also buffers the charge. id take off both red and black straps/harnesses, and clean everything up, i use electronic cleaner, with some wet or dry sandpaper, like 440 grit, a wire brush can do a lot, get a tig brush from a welding shop, get new washers and nuts/bolts for connections. i added grounds, 1 from trans top/main ground to top of alt, then one from alt top to fuel filter mount, good meaty connection. clean everything up, add more grounds cannt hurt, and the body ground at the strap too,

[mtrans]

Even if the battery is practically dead it should still put out over 13v at idle shouldn't it?

motor off - 12v empty /12.7 full
motor on - 13.7 min
If one cell is short or something like it will ruin alternator,don`t ask how I know

[RunninWild]

I don't think the grounds are the issue. Both my battery clamps are new. I even tried hooking a jumper cable to the engine as an additional ground but didn't help either.

Thanks for the offer for the regulator but it's a gm alternator, I don't think the vw one would fit?

I've basically temporarily bypassed every part of my stock wiring in the system. Could it be possible both alternators are both defective in the same way? Like can they put out a charge but once there is a load (charging the battery) it just craps out?

[ORCoaster]

Well the odds would be high on that but it is a possibility.  Pulling the batt wire while running it a no no in my book.  It isn't a welder and it needs for that juice being cranked out to have a home. 

Not sure what to say at this point in time.  Back to a known good alternator?  Take the current on to the auto parts store and have them load it up and check it out.  If it works on the bench then possibly you can take it back and get it to work in the car. 

You have to make sure the alternator is sound and functioning, I guess that is my suggestion.

[RunninWild]

Yeah I think your right. Time to call a few places and see if any local places can test it.

[libbydiesel]

Do you have the exciter wire hooked up to the alt?

[RunninWild]

Yeah the exciter is wired onto the 12v post on the back of the alternator which is wired up to the battery through the stock wiring harness.

[RunninWild]

Just had my battery and the alternator bench tested and they both came back good.

The alternator guy seemed to think it might be an issue with my wiring so I've made 100% sure it's correct.

Pin 1 is wired into the dash light. Key on engine off I get 0v there and the dash light comes on, key on engine on I get slightly less than battery voltage and the dash light turns off. This is what I should be seeing according to the alternator guy...

Pin 2 is wired back onto the 12v post on the back of the alternator I'm getting battery voltage there at all times.

This doesn't make any sense. How could the alternator work on a bench but not in my truck. I'm almost certain if I pull the positive lead it will show around 14v until the point I put it back in my battery. I'm not going to do that as I can't afford to kill this alternator...

[air-cooled or diesel]

again back to my grounding and wiring advice, running new &cleaning up grounds can help a lot. what i had stressed was motor to body ground, as well as other grounding. (&from batt teminal to body,2).

[RunninWild]

I just disconnected all my relays and accessories off of my battery terminal.

I also just took some heavy gauge jumper cables and hooked some temporary grounds with 2 on the engine, 1 on the body and 1 on the battery with no change in output. I also just removed the alty and grinded the chrome plating off the mounting surface.

Between my negative terminal and the housing on the alternator I have between 0.1 and 0.2ohm (it bounces back and forth depending where I measure)

Between my positive terminal and the 12v post I have 0.1ohm resistance. My cables are old and they should be replaced but I don't think they are the cause of the issue at this point.

I think the biggest clue is the alternator outputting 14.4v when it was disconnected from the battery. As soon as the lead was reconnected voltage dropped back to battery voltage. Anyone have any idea what would cause this? Its like some kind of feedback or interference is forcing the alternator to power off.

[ORCoaster]

Are you just measuring the voltage going to the battery when the car is running at idle?  How many accessories are you turning on.  I have seen my alternator need to see a pretty heavy load at times to get it to start pumping up the voltage and amperage.  I measure both one with a digital meter across the terminals and the amps with a clamp on style digital around the positive wire going to the battery.  I start with the fan,  low, med, then high.  Any differences? 

Then the lights, parking, low beamers then highs and then hold up on the lever to keep both on.  I set the clamp on one so I can see it under the hoodline when it is raised up.

Maybe you will see it working as you start flipping stuff on and off.  No do not flip off the alternator, you already know it is good so contain that frustration.

Give us some details on the voltage/amp changes.  It might just be a regulator that needs to have more drawing on it to up the juice.

[RunninWild]

For the most part everything is off. At one time I had the rad fans on but that was about it. So far I've only been measuring voltage as I don't have an ammeter

I'm starting to think something is going on with my trucks wiring. Tomorrow I'm going to run a new cable from the alt to the starter and a fresh one from the starter to the battery. That way I can bypass the entire stock system once it's running without hurting the alt. If that works I think I'm going to try hooking things up one at a time until it cuts out again and hopefully be able to pinpoint what part of my system is causing issues.