For any alternator to charge it has to be excited by a stimulus wire which will be one of the wires from the wiring harness, basic procedures to locate this problem are as follows , check total battery voltage and then check voltage at back at alternator, is it the same? if much lower then total battery voltage then check the connections on starter motor as some alternators have the main charge lead going to the post on the starter motor some models have a cable direct to the battery via a fusible link but mostly they are excited by the return wire from the charge light from the dash, if voltage is within .1 of a volt then positive lead connections are good, next step is to check if the stimulus wire has voltage going to it it will most likely be a red wire in among 2 others in the plug on back of the alternator,the stimulus wire voltage should be the same as battery voltage if not then check your charging system fuse and or fan fuse as this system uses the same fuse to excite the alternator , and or connectors for corrosion , if you have same voltage or within .1 of a volt then stimulus is good, next step is to check while running check total voltage at battery(reference voltage) then check voltage out of the alternator, if voltage while running should be (with no load and battery in good condition ) 13.9 to 14.2 any higher and the battery will boil and ruin the battery any lower than 13.3 and the battery cannot keep up with demand by the electrics on car. if the alternator is putting out good voltage it maybe that its not producing enough current(amperage) to maintain battery and electrical use on car. if voltage is consistently draining from battery while running there is another side to this problem which is frequently overlooked the grounding system, you can have good voltage going to positive side of battery but not be able to get enough amperage in to maintain or charge a battery if the grounding system is corroded or in poor state it can mess up your readings as well, the fact that your light on the dash is not illuminated while running is telling me your alternator is charging as it requires 12.5 volts minimum to keep charge light off, so i am thinking your charge system is doing what it should but you have a grounding issue to test this theory it only requires you to put a heavy gauge wire from body of alternator to the battery direct if the voltages become good at back of alternator and battery then you need to find the grounding problem and rectify, if they dont correct with this action then you will need to dig further into the stimulus wire you can also make a jump wire from battery to the stimulus wire on alternator to test this theory and it will also eliminate the alternator as bad if it rectifies it then you will have found the system causing the problem then you will need to find why that system is faulty(most likely corrosion on a main harness plug on the fire wall or similar place)if you follow these steps you will eliminate 5 of the 6 most common causes of charge system failures, i have been a mechanic for over 30 yrs and have seen some funky stuff that has baffled me but this should help narrow your search for causes and perhaps fix them all machanical work is a process of elimination once you have found the system effecting the normal functioning then you can hunt down the reason it wont be a guessing game anymore good luck

 

Umm 2017 post

 

As for the original poster , this thread was 2012 , and it sounds like the car didn't survive . The thread was then bumped in 2013 and again in 2017 , so I guess with this latest bump it's a three time thread necro