Brand New Alternator not charging
 

I have a 99 4x4 Dakota with a 318.

Recently my water pump bearing went out sending a mass of coolant all over the engine bay. After replacing the water pump tonight I fired the truck up and the alternator wasn't charging. Figuring that the coolant got into the electronics of the alternator I had my wife make a flying trip to the Auto parts store and bring back a new alternator. After putting the new one in the symptoms are the same. No charge. Most likely the old alternator was fine, but that is a $200 error I really don't want to talk about.

Anyway, as best I can figure the alt is not getting a power signal to charge. Where does this signal some from? What can I check to determine if it is getting a charge signal? Can I force a charge signal somehow? Should the two signal wires read a charge when the key is on or running?

Any help is appreciated. I live in kind of a boondocks town and the nearest Dodge Dealer is more than a fully charged battery's worth of drive away.

did you try the good ole alt test?


02 dakota cc 3.9
flowmaster duals
"homemade" CAI
TB spacer (expensive doorstop)
MSD Ignition

Which test would that be? I have measured voltage at the B+ terminal on the back of the alternator and I get battery voltage (which at the time was in the 11 volt range) That tells me the alt is definitely not charging. I want to test the signal wires with my DMM but don't know when and how much voltage they should be outputting. I also read in my manual about isolating the alt by grounding the negative signal wire but am not sure which one of the 2 signal wires is the negative.

i believe he's referring to pulling the negative battery cable to see if the engine still runs which you should NEVER do on a computer operated engine. you will kill off the computers.

Damn computers....

it wont kill the computer if u just do it quick dont drive it around like that, thats what hurts em'

all it takes is for the computer to be killed off is simply unplugging it. if you do this method and works for you, fine. i dont care how you fix your truck, but dont be telling others the improper way to do something. when giving other members advice on this board, it better the right advice. cause they can hurt themselves or damage their vehicle if they are not being cautious when working with electrical systems.

as for arnard, go get yourself a chilton manual. it has the wiring diagram, and has a troubleshooting section in the front of the book.

Never disconnect the battery while the car is running.. That is a sure-way to kill an ECU or damage wiring.

You need to grab a volt-meter to solve this one. It'll save you a HUGE headache in the end.

While the truck is off, ground the black probe (any unpainted metal on the truck will do fine) and touch the red probe to the positive battery terminal. Take note of this reading (should be 11v-12.4v)

Start your truck, and repeat. Your voltage should be 13.5v-14.5v or else your battery is not charging.

If you find out your battery isn't charging, you need to see if it is the alternator or the wiring.

Start your truck, ground the black probe and touch the red probe to the back of the alternator where the positive connects to the alternator (forgot the exact word for it). If you reading is less than 13.5, you have a bad alternator. You said you bought a brand new one, but even the ones you get from Parts Stores aren't always good. It took me 3 tries to get a good alternator for my Nissan (first one didn't charge, second one had a bad bearing).

If your alternator tested good, then it is a wiring problem. Verify with an FSM (Factory Service Manual, DO NOT USE CHILTONS! They have the most inaccurate wiring diagrams I've seen) that you correctly hooked up the terminals on the back.

Another possibility is that the ground to your alternator just sucks. It happens, and also another problem I went through with my Nissan. It doesn't hurt to run a ground cable from the alternator to an unpainted part of the chassis.


Hope this helps!

There is also a fuse that goes between the alternator and the rest of the wiring in your truck. I blew mine out and thought it was the alternator so I spent $200 replacing that to find out it was a $5 fuse. But its ok the bearing was going anyway.

well man i guess you just know everything about anything