Battery light is on and no power going from alternator to the battery

REBELANGEL

MEMBER
1998 PLYMOUTH VOYAGER
100,000 MILES

The battery light come on when you first start it and gose out. Then after under 3 minutes. It comes back on. Have replaced the battery and the alternator, and dont have poower going from the alternator to the battery. Have power in the wire for about 2 seconds then it gone in the wires from alternator to the battery.
can you tell me what the problem is.

3 Replies

CARADIODOC

MECHANIC
33,871 POSTS

If you're referring to the small wires on the back of the alternator, there should be voltage there for one second after turning on the ignition switch, then again during engine rotation, (cranking or running). The system can be diagnosed by measuring those two voltages while the engine is running. One will have full battery voltage. The other one must have less but not 0 volts. 4 - 11 volts is typical. If it's 0 volts, the brushes are worn. That is often intermittent so you have to check it while the problem is acting up. If you find exactly the same voltage on both wires, there's an open circuit between the second brush and the voltage regulator in the Engine Computer.

Also check for battery voltage at the output terminal when the engine is not running. If you find 0 volts there, the large bolt-in fuse in the under-hood fuse box is blown.