Battery

BARNT_08

MEMBER
1999 MERCURY COUGAR

My car was acting up and every time my RPM's would reach 3000 my lights would dim and my battery light would go on until my RPM's went down. Finally the car just died on me. I took the battery in and had it tested and it turned up bad. I bought I new battery and replaced it and went to drive and it was doing the same thing, so like most people I thought I was the alternator so I took it and had it tested and it tested out fine. I hooked it up to an error coder and it didn't bring up and codes that would relate to the battery or have anything to do with how the car was acting up. I have done all the work on all my cars and never had anything like this happen and I'm stumped. I have ran every test I can and still can't find the problem. Does any one have any other ideas that I haven't tried?

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

This is not uncommon when the regulator has failed. We need to do two things first. That is test the battery and alternator as the vehicle sits.

This will ensure both are good from the start.

https://www.2carpros.com/articles/car-battery-load-test

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Once we know they are ok then we can move onto testing the voltage across the battery when the engine is running.

This should be 14 volts. If it is not then the regulator has failed on the alternator. I attached the info below. I understand you replace the alternator already but if it has failed again, the we may have a greater issue but we need start with this.

Please run through this material and let us know if you have other questions. Thanks

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