No output from alternator

[Conflict]

Advance says its a good alternator. It's got 12v coming in but nothing coming out. How can this be? It's an 01 crown vic.

 

[lil_Blue_Ford]

If it’s not putting out about 14.4 volts, then the alternator is bad. I don’t trust Advance with testing stuff, I had one of their batteries that died under warranty. I’m no noob, so I checked it, put it on my trickle charger overnight, tested it again, verified an internal short that was causing it to self-drain, left it overnight in the cold in the truck and took it to them to warranty after work the next day. They “tested” it three times and their “tester” said it was a good battery… I explained that it simply wasn’t possible as the battery had already froze into a block of ice (middle of winter). Took dragging their commercial manager out of his back office to confirm the battery was junk because it “tested” good.

Autozone also will test alternators and the like, I’d try getting some confirmation. I’d also inspect the wiring in the vehicle and check the main fuse under the hood.

 

[Shran]

If it tests good then my guess is you have a fuse or fusible link blown somewhere. Alternators need power in order to make power so you need 12v at the excitor terminal, if you don't have that then they will do nothing but spin.

If your battery is very low then it's possible that you will see way less than the normal ~14.x charging voltage until the battery recovers. I just dealt with this last week and the battery voltage read 13-13.2v for quite a while until it had ran long enough to charge the battery. Now all is good and it is steady at around 14.2v

See this:

Ford Crown Victoria Alternator Wiring Diagrams

 

[Conflict]

Yea I verified power coming in on the #3 pin. So the alternator is being told to send out power. The battery is at 12.5 and the alternator output just reads the same while running. So it's doing nothing and there's no other conclusion than a bad alternator. Advance must be wrong. Right?

 

[lil_Blue_Ford]

Yea I verified power coming in on the #3 pin. So the alternator is being told to send out power. The battery is at 12.5 and the alternator output just reads the same while running. So it's doing nothing and there's no other conclusion than a bad alternator. Advance must be wrong. Right?

That sounds like it’s getting signal but not turning on to me…

 

[Curious Hound]

Try replacing the regulator.

 

[sgtsandman]

The idea of replacing the regulator sounds right to me. If it is bad, power going in but not coming back out seems to point to the regulator.

 

[Conflict]

Is the regulator internal to the alternator? Got a new alternator and same thing is happening. Nothing out. Is the 12v on pin 3 pulsed or just continuous 12V? It doesn't matter what's happening with pin 1, right? I have the 6G alternator.

 

[Conflict]

OK, further research on pin 1:
"Power from the ignition switch passes through the battery warning light and then to the alternator exciter circuit."
My fuse 14 supplies that and it's good. So what does that signal look like, probably some fancy signal that comes from a computer and I cant test it without a diagnostic computer. Can't I just hotwire the dam thing?

 

[lil_Blue_Ford]

Signal should be… 12 volts, because that’s usually the answer. Some alternators require a certain RPM to turn on. I ran into that with my farm tractor. New alternator but it won’t turn on at idle on the tractor. Kick the throttle up a bit and the alternator starts doing its thing and I can idle back down and it stays working. I’m using a GM “one wire” (it has three wires) alternator though so I don’t know if that applies. Also most vehicles have a higher idle speed than my 1950 farm tractor, lol

 

[Curious Hound]

"Power from the ignition switch passes through the battery warning light and then to the alternator exciter circuit."

Like lil blue said, it really is that simple. 12volts from ignition switch through warning light to alternator.

 

[Conflict]

I just sent power through my test light to pin 1 to simulate the ignition/idiot light circuit. Cranked it and the test light stayed on, just like the dash light. Then I took the light out of the circuit. 12V straight to pin 1. Alternator immediately started putting out power. WTH? You guys say it needs 12v on pin 1 and it was reading 12 the whole time. That's what was confusing. But it's the resistance thats somehow the culprit. How do I fix that? Would I hurt anything just leaving it hotwired?

 

[lil_Blue_Ford]

Sounds like there’s not enough power even though you’re reading 12v. Something must be bad in that circuit. Wire shorting somewhere or corrosion or something.

Leaving it hotwired would leave the alternator “on” all the time, which could drain the battery when it’s not running. If you’re going to “Hotwire” it, you need to pull power off a key-on power source so when you’re key off the alternator is “off”

 

[Conflict]

Well I've got 2 alternators. The trick worked on the new alternator but I put the original back in and straight wired power to pin 1. It came on for a few seconds then quit. Maybe I fried it. So maybe some resistance is required to not do that. Anybody know?

 

[lil_Blue_Ford]

The way my farm tractor is wired is as simple as it gets for power on signal. I pulled key-on power, put it through an LED dash indicator light (the alternative here is to add a diode, but since an LED is a diode, simple as that). Negative side of the diode goes to the alternator, positive side to key-on power. This ensures that you have a clean signal flowing one direction only (the alternator can’t backfeed the circuit because the diode only lets electricity go one direction).