Have a ford 555d that the alternator started to lock up and broke the belt. Alternator spun but was hard to turn. Replaced the alternator and belt. Started machine up and it isnt charging. Noticed that the warning light did not come on with the key on. Pulled the wire at the alternator for the light circuit and ground it and the light came on so the warning circuit is okay. Checked voltage at the B+ wire and it was battery voltage. When the engine is running I have battery voltage at the warning light, the B+, the black wire beside the B+. The last wire only has .6 volts on it with the engine running or not with the key on. I am wondering if that should have half voltage to excite the alternator or do I have a bad alternator.
I'd need a picture of the back of the alternator to guess better. But I'd start by hooking 12V to any terminal that is not obviously a ground, or "W" for the tachometer (if it's not a cable driven tach). Then see if it charges. Alternators usually aren't that complicated unless you get into external voltage regulators, which is somewhat unusual.
I have put another alternator on and it is still not charging. I have voltage on the indicator terminal and the B+ terminal. There is another wire that is on here besides the W terminal that I am not sure what it is. I also think that this has the regulator on the alternator. I will post a picture of the wire i am not sure about.
well i found out the problem. There is a battery sensor that was unplugged by the battery. Customer had put a battery in it but i dont think they did anything to it. Resistance on the sensor was 214 ohms. Got everything back together and the battery light still does not illuminate but it is charging.
If the battery light illuminates it means your alternator is not charging. So being off is a good thing.
The alternator light usually means that current is flowing through the bulb. If everything is hooked up correctly, the alternator voltage when charging should equal the ignition side and the bulb goes out. Current flowing either way will keep the bulb on.
Saw this too late. I was going to suggest that you check the temp sensor by the battery. It seems to be a pretty common problem.