After replacing the alternator with a new/used one the engine idles poorly and when the truck is turned off with the keys removed my battery light will stay on?

2002 FORD EXPLORER

200,000 MILES • 4.0L • 6 CYL • 2WD • AUTOMATIC

GIGI74

MEMBER
1 POST

I replaced the alternator with a used one and now my idle is bad, and when the truck is off with the keys removed my battery light will stay on and run my battery down. What can I do?

Aug 1, 2023 at 12:23 AM

STRAILER

✓Experienced Mechanic
55,554 POSTS

Yep, it sounds like you have a defective alternator that is allowing the voltage to back feed through it. To be sure disconnect the wiring from the alternator to see if the light goes off. Here is a generic guide to help you step by step with instructions in the diagrams below to show you how on your car:

https://www.2carpros.com/articles/how-to-replace-an-alternator

Check out the images (below). Please let us know how it goes

Images (Click to enlarge)