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Chris (aka- Moose)
Chris (aka- Moose), Mercury Technician
Category: Mercury
Satisfied Customers: 1972
Experience:  16 years experience with Mercury
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2005 Mercury Mariner alternator overcharges a battery after

Customer Question

hello, 2005 Mercury Mariner alternator overcharges a battery after I replaced the alternator.
JA: Have you tested the battery with a voltmeter? And can you see if it's leaking or not?
Customer: I checked the battery and replaced it with a brand new one once I have replaced the battery I measured and the cherge was showing good
JA: Are you fixing your Mariner yourself? What have you tried so far?
Customer: Changed the alternator, changed a battery
JA: Anything else you want the mechanic to know before I connect you?
Customer: the overcharge does not happen all the time, usually after the car is driven for a while
Submitted: 2 months ago.
Category: Mercury
Expert:  Mechanic01 replied 2 months ago.

Hello my name is ***** ***** I will be assisting you with all of your vehicle questions today. Give me one moment while I review your question and come back with a answer. Please be aware I do not know your skill level or abilities so I will be asking a lot of questions and in a lot of cases we will respond to each other quite a lot before we find a solution. As far as phone calls are concerned that is the system prompting you, not me, and they do cost more money, I prefer text but in some cases a phone call is required.

Expert:  Mechanic01 replied 2 months ago.

Can you elaborate on the over charging and what voltages your getting?

Customer: replied 2 months ago.
Last night, after replacing the battery I was getting 14.6 volts @1500 RPM; today, after driving the car for 18 miles, the battery light came on, the instrument cluster started going off every time I press gas, the reading was at about 17 volts
Customer: replied 2 months ago.
I feel like the regulator is not getting the correct reading, but I do not understand why is this happening only after the car is driven for a bit.
Expert:  Mechanic01 replied 2 months ago.

Sounds like a bad regulator in the alternator, but here are some system checks to verify its not something else

1. Access the alternator connectors. Backprobe the Black/Yellow (BK/YE) wire on the 2 wire connector. Monitor the voltage on this circuit when the problem is occurring. The BK/YE wire should maintain full charging system voltage at all times and is fed from fuse #11 15A in the engine compartment fuse box. If the voltage is low when the problem is occurring, repair the circuit and recheck operation. Also verify the terminal connections between the harness and voltage regulator are clean and tight.

2. If the voltage on the BK/YE wire is good, monitor the voltage on the output terminal of the alternator, again when overcharging, to verify it shows the same voltage as at the battery. If the voltage is different, repair the circuit and recheck operation.

3. If both circuits show the correct voltage but the alternator is simply overcharging, suspect a faulty alternator.

Customer: replied 2 months ago.
what do you mean by "repair the circuit"?
Expert:  Mechanic01 replied 2 months ago.

that would indicate there is a fault in the wire itself and it would need to be repaired and retested

Customer: replied 2 months ago.
In #1 and #2 is the engine running?
Expert:  Mechanic01 replied 2 months ago.

yes

Customer: replied 2 months ago.
When using voltometer, am I probing BK/YE at the same time with red and black probes of the votometer?
Customer: replied 2 months ago.
Also , it looks like fuse #11 is 10 AMP PCM
Expert:  Mechanic01 replied 2 months ago.

the black should be ground and red for probe,

Customer: replied 2 months ago.
I am still not clear as to why overcharging occurs only after driving the vehicle for a period of time.
Expert:  Mechanic01 replied 2 months ago.

this is why were doing the testing, its prob a bad alternator,