no output from brand new oem alternators

I have an 87 b2200. new optima red top, new alternator, new belt and still the alternator won't charge the battery. i thought maybe it was a bad alternator, so i changed it and still have the problem after changing out three new alternators. i put the new belt and battery when i did the tune up and the truck ran fine with no problems, it charged fine and everything, the funny thing is, this problem started after i got my gas gauge working. does anyone know what could cause this problem?

do you have a volt meter? the battery should have between 11 and 12volts while the truck is off. and closer to 12 to 13 volts when its charging (with the truck running). maybe you have a bad connection somewhere either at the battery or on the alt???



on a side note. still have receipt for the battery? try swapping it out. i know that even brand new batteries can have burnt cells. and will act very strange. i recently had a yellow top that would charge, then while the truck was running it would discharge. changed back to my duralast battery and haven't had a problem since.

check to see if your getting 12+ volts with the key turned on at the 2 pin plug that plugs into the back of the altenator, one pin is ignition and the other one goes to the dummy light i think
if anyone else has any different info hop in!!

One wire is black w/white stripe, the other is white w/black stripe.
The black w/white stripe should have 12v. when the key is in run.
It "excites" the regulator.
Without this reference voltage, the alternator won't charge, no matter how much it spins.

So... look for a break in that circuit.
I had a problem with this about a year ago.
The wire appeared fine, by the looks of the insulation, but the wire inside was broken.
It would have a connection at times, but with a bump or a vibration it lost its connection.
It was a real bitch to figure out!

i had the battery tested and recharged at advance auto parts where i bought it and they said it was fine, but while the optima battery was there i was using a new autostart silver and still had the same problem. my dad told me to start the truck and while its running to disconnect the battery...if the truck keeps running then the alternator is good, if it dies then the alternator is bad...i tried that and the truck shuts off as soon as i remove the battery cable. i checked the volts with the truck running and not running and its the same 12.2 volts. the truck did the same thing with three new alternators. i even took off all the wire loom and tape to check the wires going to the alternator but everything looks good. maybe in a couple of hours i can take some pics outside so you guys can see what i have, maybe i have something plugged in wrong

check your fuses, and look at the connections in the plastic connector, I fought that issue with a dodge neon at work. It came in dead, i charged the battery got it running. It wasn't charging so I put new alt on and it did the same thing. It ended up bein the little metal connectors on the ends of the wires had been hogged out and wasn't making a connection and not charging. I will look at some wiring diagrams at work tomorrow to see whats all tied in the system, hopefully i'll be able to help ya

ive always heard its bad to do that, dissconnect the battery while a vehicles running. its better to test everything with a voltage meter as i stated in the second post here. without key on should be close to 12volts, when the trucks running (if all is working right) should be 12+ volts.

from what you posted about the test results the alt isn't putting out. i dont think swapping it out again is going to help. obviously something isn't hooked up or has a bad/broken connection. also as stated above. the wiring colors. "The black w/white stripe should have 12v. when the key is in run." try testing that with your volt meter.

I posted the schematic for the charging system for your truck here:

Your going to have a bad connection in the electrical connector of the alternator, or a bad wire, or a bad ground after lookin at the electrical diagrams. Double check those three things, I bet you one will fail

the two wire plug (with the black w white stripe and white w black stripe) is for the regulator.
the 8 or 10 guage wire bolted to the stud on the back is for recharging the battery.

so what are the other two wires for?

theres one red wire with a female terminal inside the plastic clip. i was told that its for the electric choke.

and one lonely yellow wire with a female terminal plugged in at the bottom of the alernator is for???

BTW... thanks for all the help so far, i had my truck sitting for about four years while i helped everyone else around me build their projects, now i finally get mine drivable and it dies on me after two days, so its been sitting for like three months again