Electrical problem going to alternator

JONATHAN KETCHUM

MEMBER
2000 CHEVROLET SUBURBAN
5.4L
V8
2WD
AUTOMATIC
170,000 MILES

Battery light comes on, and it will drain the battery until dead. It has a new battery, new alternator and new PCM. It is sporadic. Sometimes when tested, the charging system test good, sometimes not. It was hard to track down because this, but I finally figured out that the wire that energizes the alternator is going in and out. It test good sometimes, has no voltage sometimes and is low on voltage sometimes. I checked that wire for continuity and it’s good as far as from the PCM to the alternator. Not sure what to do next?

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,772 POSTS

Hi and thanks for using 2CarPros. Com.

From experience, I have found that existing continuity can provide a false positive. Basically, when checking for continuity, the power that goes through the wire being tested is so minimal, it checks good. However, when a load is placed on the wire, it fails.

I have a suggestion. Purchase a generic light bulb socket at the parts store, something like a back up light socket, and make sure to get a good bulb. Disconnect the wire in question and basically, using the car's battery, make a circuit which requires power to go through the wire in question and the newly purchased socket. By doing this, you are placing a load on the wire. If the bulb fails to light or is extremely dim, replace the wire.

Try this and let me know what you find.

Take care,
Joe