Electrical systems can be finicky and sometimes just replacing parts isn’t enough to diagnose this issue. Car Doctor John Paul has some advice:
Q. I have a Honda Accord and the battery died. I replaced the battery and it died again. I had the new battery tested and while it was being tested, the parts store checked the alternator and told me to replace it. I put a new alternator in and the charging voltage went from 12.3 volts up to 14.8 volts but now the alternator light is on.
I took the car back to where I purchased the alternator and battery and they told me that everything is fine. If everything is fine, why is the alternator light on? My friends are telling me the issue is that it is a rebuilt alternator an not a Honda alternator. Can you give me some direction on this?
A. There are two possibilities, the replacement alternator could in fact be defective. Rebuilt alternators vary in quality. In some cases the alternator is cleaned disassembled and only the worn component is replaced. In other cases the alternator is disassembled and the bearings, brushes and other components are replaced.
One issue that I have seen is, that it is not unusual, if a group of alternators are rebuilt they can all be defective because the replacement parts all came from the same supplier. If you can talk the parts store into replacing the alternator, ask for a different brand to eliminate this possibility.
The other issue is that during the replacement you broke a wire. Typically the light is powered by a fuse and when a ground is applied to the alternator is will turn the light on. The possible issue could be that the wiring may have chaffed through after wiggling it around during the installation and is now grounding the circuit and keeping the light on.
I would start with wiggling the wires and see if you can get the light to flicker. If the light flickers a careful inspection of the wiring should solve the problem.
John Paul is public affairs manager for AAA Southern New England. A certified mechanic, Paul tests dozens of new cars each year and also hosts a radio show on AM 950 and 550.